KR20050016856A - Coated current collector for reducing self discharge and sulfur battery using same - Google Patents

Abstract

PURPOSE: Provided are a current collector having decreased self discharge and a sulfur battery with good discharge capacity by applying such current collector. CONSTITUTION: The current collector is coated with at least one coating material selected from the group consisting of a metal or precious metal, a carbonaceous material and an electrically conductive polymer, which have an ionization tendency lower than an active material of an electrode. The sulfur battery includes a positive electrode comprising such current collector contained in a mixture containing sulfur-active material, an electrically conductive material and a binder; a negative electrode comprising a transition metal, an alloy thereof, or carbon; and an electrolyte between the positive electrode and the negative electrode as an ion-conductive medium.

Description

Coated current collector for reducing self discharge and sulfur battery using same

The present invention relates to a current collector coated with a more stable material than the electrode active material and a sulfur battery using the same to reduce self discharge.

Globally, development of secondary batteries used as mobile power sources for electronic products is being actively conducted.

Lithium sulfur battery is cheaper and theoretical energy density is 2600Wh / kg (1675mAh / g), which is much higher than other battery systems.

In the case of lithium sulfur batteries, lithium polysulfide or lithium sulfide is formed in the sulfur electrode when it is kept for a long time and is dissolved into the electrolyte, and a discharge capacity decreases. This phenomenon in which the discharge capacity decreases when left unused for a long time is called self discharge.

If the material of the current collector is more stable than sulfur, which is an active material, and can move electrons well, sulfur can be reduced to lithium poly sulfide or lithium sulfide, thereby reducing the discharge capacity due to self discharge.

Accordingly, an object of the present invention is to provide a current collector coated with a material having a lower ionization tendency than an active material of an electrode by a simple coating operation in order to reduce self discharge of a sulfur battery.

Another object of the present invention is to provide a sulfur battery having excellent discharge capacity by applying the current collector.

In the current collector of the present invention, a coating material obtained by selecting at least one selected from the group consisting of metals, precious metals, carbon series, such as carbon, graphite or nanotubes, and conductive polymers, which has a lower ionization tendency than the active material of the electrode, is sputtered and CVD. Or it is coated by the plating process has a feature that can reduce the self-discharge of the sulfur battery.

In addition, the present invention is a positive electrode comprising a current collector in a mixture of a sulfur-containing active material, a conductive material made of carbon or a conductive polymer and a binder made of a polymer: a transition metal (Li, Na, Mg) or transition metal A negative electrode made of an alloy, carbon or the like is a sulfur battery comprising an electrolyte as a medium for ion conduction between the positive electrode and the negative electrode.

Preferably, the active material is at least one selected from the group consisting of sulfur molecules (S8), polysulfides (Li ₂ S _x X> 1), sulfur-carbon polymers, a solid polymer electrolyte and It is preferable to use at least one selected from the group consisting of a gel electrolyte and a liquid electrolyte obtained by adding a plasticizer to the polymer.

In particular, the polymer is a polyurethane, polyvinylidene hexafluoropropylene copolymer, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide or polypropylene oxide and the resulting composite polymer It is preferable to use at least one selected from the group consisting of, the plasticizer and the liquid electrolyte is polyethylene glycol dimethyl ether (PEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), ethylene carbonate ( At least one selected from the group consisting of EC), propylene carbonate (PC), dioxolane, sulfolane and dimethyl ester (DME) is preferably used.

The present invention will be described in more detail based on the following examples.

Example 1

The sulfur electrode used as the anode is manufactured as follows.

A ball, sulfur, carbon, and polyvinylidene fluoride (PVdF) were added and mixed in an atliter ball milling machine (man-made). At this time, the ratio of the ball and the powder was 30: 1, the ratio of sulfur: carbon: PVdF used in the production of sulfur electrodes was 50: 30: 20. Tetrahydrofuran (THF) solution was added to the mixed powder, and ball milling was performed for 2 hours. A well mixed electrode was cast to prepare a sulfur electrode.

As the current collector, stainless steel was used, and gold (Au) was coated on the surface by a sputtering method.

As the electrolyte, a polymer electrolyte prepared by adding tetraethylene glycol dimethyl ether (TEGDME) and a lithium salt to polyvinylidene fluoride (PVdF) was used.

On the coated current collector, a sulfur electrode, a polymer electrolyte, a lithium metal, and a negative electrode current collector were stacked in this order to constitute a cell.

Comparative Example 1

A cell was constructed in the same manner as in Example 1 except that stainless steel was used as the current collector for the positive electrode.

1 is a cross-sectional view of a sulfur battery using a coated current collector according to Example 1, wherein a is a current collector of a positive electrode, b is a coating layer of the present invention, and c and e are sulfur anodes and Indicates the negative electrode. d and f represent the electrolyte and the negative electrode current collector.

Open-circuit voltage (OCV) measurement

Opening voltage of the lithium sulfur battery was measured for 30 days using the cells prepared in Example 1 and Comparative Example 1, and the results are shown in FIG. 2. According to FIG. 2, the sulfur battery of Comparative Example 1 using the current collector without coating was decreased from 2.4V to 2.1V, but the sulfur battery of Example 1 using the current collector coated with gold (Au) did not decrease. .

Discharge experiment

After discharging the batteries of Example 1 and Comparative Example 1 at 25 ℃ for 30 days, the discharge capacity was compared. During discharge, the current density was 100mAh / g-sulfur and the termination voltage was 1.7V. The discharge test results are shown in Table 1 below.

Table 1

               Neglected time discharge capacity 0 days (no charge) 30 days (no charge) Example 1 100% 87% Comparative Example 1 100% 60%

According to Table 1, after 30 days of standing, the discharge capacity of the sulfur battery was reduced by 40% using the uncoated current collector (Comparative Example 1), and the current collector coated with gold (Au) (Example 1) Decreased by 13%.

Example 2

Except for using a liquid electrolyte prepared by adding tetraethylene glycol dimethyl ether (TEGDME) and lithium salt as an electrolyte to impregnated in the cell-movable cell guard, it was carried out in the same manner as in Example 1 except that the sulfur electrode, liquid electrolyte on the current collector (Impregnated with Celgard), lithium metal, and a negative electrode current collector were laminated in this order to constitute a cell.

Comparative Example 2

A liquid electrolyte prepared by adding tetraethylene glycol dimethyl ether (TEGDME) and a lithium salt as an electrolyte was used in the same manner as in Comparative Example 1 except that the liquid electrolyte was impregnated into a lithium-movable cell guard. (Impregnated with Celgard), lithium metal, and a negative electrode current collector were laminated in this order to constitute a cell.

Measurement of the open circuit voltage (OCV)

Opening voltage of the lithium sulfur battery was measured for 30 days using the cells prepared in Example 2 and Comparative Example 2. The results are shown in FIG. 3. According to FIG. 3, the sulfur battery of Comparative Example 2 using the current collector without coating was decreased from 2.4V to 2.1V, but the sulfur battery of Example 2 using the current collector coated with gold (Au) did not decrease. .

Discharge experiment

After discharging the batteries of Example 2 and Comparative Example 2 for 30 days at 25 ℃ compared the discharge capacity. During discharge, the current density was 100mAh / g-sulfur and the termination voltage was 1.7V. The discharge test results are shown in Table 2 below.

Table 1

               Neglected time discharge capacity 0 days (no charge) 30 days (no charge) Example 2 100% 84% Comparative Example 2 100% 43%

According to Table 2, after leaving for 30 days, the discharge capacity of the sulfur battery was reduced by 57% using the current collector (Comparative Example 2) without coating, and the current collector coated with gold (Au) (Example 2) Decrease by 16%.

When using a current collector coated with a metal or an electrical conductor more stable than the electrode active material of the present invention, self-discharge can be reduced, thereby improving the discharge capacity of the lithium sulfur battery.

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

2 and 3 are graphs showing the results of measuring the open-circuit voltage of the sulfur battery of the embodiments and comparative examples of the present invention.

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

a: positive electrode current collector b: coating layer

c: sulfur anode d: electrolyte

e: negative electrode f: negative electrode current collector

Claims (8)

A current collector, characterized in that the coating material is coated with at least one selected from the group consisting of metals, precious metals, carbon series, and conductive polymers having a lower ionization tendency than the active materials of electrodes for reducing self discharge of lithium sulfur batteries. The coated current collector of claim 1, wherein the carbon-based material is carbon, graphite, or nanotubes. The coated current collector of claim 1, wherein the coating is performed by a sputtering, CVD, or plating process. An anode comprising a current collector according to claim 1 in a mixture of an active material comprising sulfur, a conductive material made of carbon or a conductive polymer, and a binder made of a polymer: A negative electrode made of transition metals (Li, Na, Mg) or alloys of transition metals, carbon, or the like: A sulfur battery comprising an electrolyte as a medium for ion conduction between the positive electrode and the negative electrode. The sulfur battery according to claim 4, wherein the active material is selected from the group consisting of sulfur molecules (S8), polysulfides (Li ₂ S _x X> 1), and sulfur-carbon polymers. The sulfur battery according to claim 4, wherein at least one selected from the group consisting of a solid polymer electrolyte, a gel electrolyte obtained by adding a plasticizer to the polymer, and a liquid electrolyte as a medium for ion conduction. The method of claim 6, wherein the polymer is polyurethane, polyvinylidene hexafluoropropylene copolymer, polyvinylidene fluoride, polyvinylchloride, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide or polypropylene oxide and Sulfur battery, characterized in that by selecting at least one from the group consisting of a composite polymer. The plasticizer and the liquid electrolyte of claim 6 are polyethylene glycol dimethyl ether (PEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), ethylene carbonate (EC), propylene carbonate (PC), dioxolane Sulfur is a sulfur battery, characterized in that at least one selected from the group consisting of dimethyl ester (DME).