KR20180031833A - Separator for sodium ion rechargeable battery and sodium ion rechargeable battery comprising the same - Google Patents

Abstract

According to the present invention, disclosed are a separator for a sodium ion battery, in which a tetraethyl orthosilicate (TEOS) is coated on a surface of the separator to improve wettability of an electrolyte and to promote smooth movement of sodium ions, and a sodium ion battery including the same. The separator of a sodium ion battery of the present invention comprises: a separator base material composed of a polyolefin-based compound; and a coating film formed by coating the TEOS on the surface of the separator base material.

Description

[0001] The present invention relates to a separation membrane for a sodium ion battery and a sodium ion battery including the sodium ion battery,

The present invention relates to a sodium ion battery, and more particularly, to a separator for a sodium ion battery and a sodium ion battery including the same, wherein the separator is coated with a surface thereof to improve wettability with an electrolytic solution.

As consumers' demands have changed due to digitization and high performance of electronic products, market demand is changing due to the development of batteries with high capacity due to thinness, light weight and high energy density. In addition, in order to cope with future energy and environmental problems, development of hybrid electric vehicles, electric vehicles and fuel cell vehicles has been actively promoted, and it is required to increase the size of batteries for automobile power sources.

Lithium secondary batteries have been put to practical use as batteries that can be miniaturized and lightweight and can be recharged with a high capacity, and are used in portable electronic devices such as portable video cameras, mobile phones, and notebook personal computers and communication devices. The lithium secondary battery is composed of a positive electrode, a negative electrode and an electrolyte. The lithium secondary battery functions to transfer energy while reciprocating both electrodes such as lithium ions from the positive electrode active material charged into the negative electrode active material, This is possible.

Recently, research on sodium-based secondary batteries (hereinafter referred to as "sodium ion batteries") using sodium instead of lithium has been reexamined. Since sodium is abundant in resource reserves, secondary batteries can be manufactured at low cost if sodium secondary batteries can be manufactured instead of lithium.

Polyethylene (PE) or polypropylene (PP) separator is used for the lithium ion battery. However, when it is applied to a sodium ion battery, it is difficult to achieve battery performance because it is not wetted with the electrolyte solution .

Therefore, there is a demand for a separation membrane excellent in compatibility with an electrolyte solution used in a sodium ion battery.

Korean Registered Patent No. 10-1546877 (Aug.

Disclosure of Invention Technical Problem [8] The present invention provides a separator for a sodium ion battery and a sodium ion battery including the separator, wherein the separation membrane is coated with tetraethyl orthosilicate (TEOS) on the surface of the separator to improve the wettability of the electrolyte, The purpose is to provide.

In order to achieve the above object, a separation membrane for a sodium ion battery according to the present invention includes a separation membrane base material made of a polyolefin-based compound and a coating film formed by coating a surface of the separation membrane base material with tetraethyl orthosilicate (TEOS).

Further, the separation membrane base material is characterized by comprising polyethylene (PE) or polypropylene (PP).

The separation membrane base material is immersed in a mixed solution of acetone and benzoyl peroxide (BPO) for 30 minutes to 2 hours, followed by naturally drying at 15 to 25 ° C.

Also, the coating film is formed by immersing the separation membrane base material in a TEOS solution, followed by heat treatment at 80 ° C to 100 ° C.

And a wetting angle of 50 DEG or less.

A sodium ion battery according to the present invention comprises a cathode containing a cathode material for storing sodium ions when discharging, a cathode containing a cathode material for storing the sodium ions when charged, a cathode containing the sodium ion between the anode and the cathode, And a separation membrane containing a coating film formed by coating with TEOS on the surface of the separation membrane base material and a separation membrane using the sodium salt as a medium for transferring the sodium ion to the anode and the cathode, sodium salt).

The electrolyte is characterized in that sodium perchlorate (NaClO ₄ ) or sodium hexafluorophosphate (NaPF ₆ ) is added to a solvent in which propylene carbonate (PC) and ethylene carbonate (EC) are mixed .

The separator for a sodium ion battery and the sodium ion battery including the same according to the present invention can improve the wettability of electrolyte by coating TEOS on the surface of the separator, thereby promoting smooth migration of sodium ions and improving electrochemical characteristics.

1 is a schematic view showing the structure of a sodium ion battery according to the present invention.
FIG. 2 is a view showing the wetting angle of the separation membrane before and after the coating of the coating film according to Examples and Comparative Examples of the present invention. FIG.
FIG. 3 is a scanning electron microscope (SEM) image of a separation membrane before and after coating of a coating film according to an embodiment and a comparative example of the present invention.
FIG. 4 is a graph showing an electrochemical performance evaluation of a separation membrane before and after coating of a coating film according to Examples and Comparative Examples of the present invention. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals as used in the appended drawings denote like elements, unless indicated otherwise. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather obvious or understandable to those skilled in the art.

1 is a schematic view showing the structure of a sodium ion battery according to the present invention.

Referring to FIG. 1, the sodium ion battery 100 improves the wettability of the separation membrane 30 with respect to the electrolyte 40, thereby promoting smooth movement of the sodium ions 15, thereby enhancing the electrochemical characteristics. The sodium ion battery 100 includes an anode 10 containing a cathode material (cathode active material) 11 for storing sodium ions 15 at the time of discharging, an anode material 10 for storing sodium ions 15 at the time of charging A separation membrane 30 for transferring sodium ions 15 between the positive and negative electrodes 10 and 20 and a separator 30 for transferring sodium ions 15 between the positive and negative electrodes 10 and 20, 15) can be used as a transfer medium and includes an electrolyte 40 containing a sodium salt.

More specifically, the anode 10 is an electrode on which the cathode material 11 is reduced by receiving electrons from an external conductor. That is, the anode 10 includes a cathode current collector 13 for collecting electrons and sending the electrons to external leads, and a cathode material 11 having a structure capable of inserting and desorbing sodium ions 15. For example, the cathode material 11 may include a sodium metal compound. The metal compound may be composed of the oxygen ions 11a and the metal ions 11b.

The cathode 20 is an electrode for emitting electrons to the conductor while the cathode material 21 is oxidized. That is, the cathode 20 includes an anode current collector 23 for collecting electrons and sending the electrons to an external conductor as the anode 10, an anode material 21 having a structure capable of inserting and desorbing sodium ions 15, Lt; / RTI > For example, the anode material 21 may include graphite.

The separation membrane 30 may have a structure having fine pores so that the sodium ions 15 can move. The separation membrane 30 can sufficiently wet the electrolyte solution 40 described later to improve the wettability. That is, as the wetting angle of the separation membrane 30 is lowered to 50 ° or less, the wettability is improved and the discharge capacity of the sodium ion battery can be improved.

The separation membrane 30 includes a separation membrane base material 31 made of a polyolefin based compound and a coating film 33 formed by coating the surface of the separation membrane base material 31 with tetraethyl orthosilicate (TEOS). The separator base material 31 may include polyethylene (PE) or polypropylene (PP).

The separation membrane 30 may be formed through the following manufacturing process. First, the separation membrane base material 31 is subjected to a pretreatment process. The separation membrane base material 31 is immersed in a mixed solution of acetone and benzoyl peroxide (BPO) for 30 minutes to 2 hours, preferably for 1 hour. After the immersion is completed, the separation membrane base material 31 is pre-treated by performing natural drying at room temperature, that is, at 15 to 25 ° C.

Next, a coating film 33 is formed on the separation membrane base material 31 having undergone the preprocessing process. The separation membrane base material 31 is immersed in a TEOS solution and then heat-treated at 80 ° C to 100 ° C to form a coating film 33, preferably at 90 ° C.

Here, the manufacturing process of the separation membrane 30 described above is only one example, and the coating film 33 may be formed on the separation membrane base material 31 through various methods.

The electrolyte 40 is a medium for causing mass transfer, that is, movement of the sodium ions 15, so that the reduction of the anode 10 or the oxidation reaction of the cathode 20 is chemically coordinated. At this time, the electrolyte 40 contains a sodium salt. The electrolyte 40 has a high dielectric constant and low viscosity. That is, since the electrolyte 40 has a high dielectric constant, the sodium salt is well dissociated and the viscosity is low, so that the sodium ion 15 can be easily delivered. Here, the electrolyte may be added with sodium perchlorate (NaClO ₄ ) or sodium hexafluorophosphate (NaPF ₆ ) in a solvent in which Propylene Carbonate (PC) and Ethylene Carbonate (EC) are mixed.

In other words, the sodium ion battery 100 is a device that converts the chemical energy of the internal active material into electrical energy by a chemical reaction. The sodium ion battery 100 has a special internal structure to allow electrons to escape to the outside through an electric wire due to an electrochemical reaction. Electrons flowing through the electric wire can provide electricity as a source of electric energy. Components of the sodium ion battery 100 include an anode 10 as an electrode on which the cathode material 11 is reduced by receiving electrons from an external conductor and a cathode 20 as an electrode for emitting electrons to the conductor while oxidizing the cathode material 21 ), The physical contact between the anode 40 and the anode 10 as a medium in which mass transfer occurs and the cathode 20 are prevented so that the reduction reaction and the oxidation reaction of the active material can be chemically coordinated and the surface of the separation membrane base material 31 And a separation membrane 30 in which a coating film 33 containing TEOS is formed.

On the other hand, the cathode 20 of the sodium ion battery 100 is a substance that gives off electrons and is oxidized. On the other hand, the anode 10 is a material that receives electrons and is reduced. When the sodium ion battery 100 is connected to the external load 50 to perform the discharge reaction, the two electrodes electrochemically react with each other and convert them into electrical energy. At this time, the electrons generated by the oxidation reaction of the cathode 20 migrate to the anode 10 via the external rod 50, and cause a reduction reaction with the cathode material 11. Therefore, the electric circuit can be completed in the electrolyte 40 by the mass transfer of anions and cations toward the cathodes 20 and the anodes 10.

Hereinafter, the performance of the separation membrane 30 according to the present invention was evaluated through Examples and Comparative Examples. When the performance of the comparative example was evaluated with a general PE separator, the performance of the embodiment was evaluated by using a PE-TEOS separator coated with TEOS on the surface of the PE separator according to the present invention. At this time, the other components except the membrane were tested under the same conditions.

Here, the PE-TEOS separation membrane was prepared as follows. First, the PE separator base material was immersed in a mixture of acetone and BPO for 1 hour and then naturally dried at room temperature. Secondly, PE-TEOS membranes were fabricated by immersing the naturally dried PE membrane base material in TEOS solution and then heat-treating at 90 ° C.

2 is a view showing the wetting angle of the separation membrane before and after the coating of the coating film according to the embodiment of the present invention and the comparative example. FIG. 2 (a) is a view showing the wetting angle with respect to the PE separation membrane, and FIG. 2 (b) is a view showing the wetting angle with respect to the PE-TEOS separation membrane.

Referring to FIG. 2, the wettability of the PE separator and the PE-TEOS separator with respect to the electrolyte was confirmed.

In FIG. 2 (a), the PE separator has a high wetting angle of 76.5 °, and it can be seen from the photograph on the upper right that the separator does not get wet with the electrolyte solution.

On the other hand, in FIG. 2 (b), the wetting angle of the PE-TEOS separator was lowered to 48.3 °, and the impregnation of the electrolyte into the separator was confirmed at the upper right photograph.

FIG. 3 is a scanning electron microscope (SEM) image of a separation membrane before and after coating of a coating film according to an embodiment and a comparative example of the present invention. 3 (a) is a scanning electron microscope image of the surface of the PE separator, and FIG. 3 (b) is a scanning electron microscope image of the surface of the PE-TEOS separator.

Referring to FIG. 3, the surface of the PE separator and the surface of the PE-TEOS separator were confirmed.

In FIG. 3 (a), the surface of the PE separator can observe native pore structures, but FIG. 3 (b) shows the surface morphology of the PE-TEOS separator. That is, the PE-TEOS separator can deduce that TEOS is coated on the surface of the PE.

FIG. 4 is a graph showing an electrochemical performance evaluation of a separation membrane before and after coating of a coating film according to Examples and Comparative Examples of the present invention. FIG. 4 (a) shows the electrochemical performance of the PE separator, and FIG. 4 (b) shows the electrochemical performance of the PE-TEOS separator.

Referring to FIG. 4, a CR2032 coin cell was prepared for evaluating the electrochemical performance of a PE separator and a PE-TEOS separator. The anode is Na _{0 . 7} Ni _{0 . 2} Co _{0 . 1} Mn _{0 . 7} O ₂ , and Na metal. The electrolyte solution was prepared by dissolving 1 mol of NaClO ₄ in a mixture of PC and EC in a volume ratio of 1: 1.

In FIG. 4 (a), the charge / discharge capacity of the PE separator was almost not exhibited, but it was confirmed that the PE-TEOS separator had a discharge capacity of about 100 mAh / g in FIG. 4 (b).

The PE membrane was not well wetted by the electrolyte solution, and it was difficult to secure the path of sodium ions between the anode and the cathode. On the other hand, the PE-TEOS membrane improved the electrolyte wettability due to the TEOS surface coating, It can be confirmed that this is possible.

Accordingly, it has been confirmed that the technique of coating the surface of the polyolefin separator according to the present invention with TEOS is effective in improving the wettability of the electrolyte for a sodium ion battery, thereby realizing performance of the sodium ion battery.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation in the embodiment in which said invention is directed. It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the appended claims.

10: positive electrode 11: positive electrode material
11a: oxygen ion 11b: metal ion
13: positive electrode collector 15: sodium ion
20: cathode 21: anode material
23: anode current collector 30: separator
31: separator base material 33: coating film
40: electrolyte 50: external load
100: Sodium ion battery

Claims (7)

A separation membrane base material made of a polyolefin series compound; And
A coating film formed by coating a surface of the separation membrane base material with tetraethyl orthosilicate (TEOS);
A separator for a sodium ion battery. The method according to claim 1,
The separation membrane base material,
A separator for a sodium ion battery, characterized by comprising polyethylene (PE) or polypropylene (PP). The method according to claim 1,
The separation membrane base material,
Wherein the membrane is immersed in a mixed solution of acetone and benzoyl peroxide (BPO) for 30 minutes to 2 hours, followed by naturally drying at 15 ° C to 25 ° C. The method according to claim 1,
The coating film may include,
Wherein the separation membrane base material is formed by being immersed in a TEOS solution, and then heat-treated at a temperature of 80 ° C to 100 ° C to form a separator for a sodium ion battery. The method according to claim 1,
Wherein the wetting angle of the separator is 50 DEG or less. A positive electrode containing a positive electrode material for storing sodium ions upon discharge;
A negative electrode containing an anode material for storing the sodium ion when charged;
A separation membrane containing a separation membrane base material made of a polyolefin-based compound and a coating film formed by coating the surface of the separation membrane base material with TEOS, the sodium ion being transferred between the anode and the cathode; And
An electrolyte containing sodium salt as a transfer medium to the anode and the cathode;
≪ / RTI > The method according to claim 6,
The electrolyte,
Characterized in that sodium perchlorate (NaClO ₄ ) or sodium hexafluorophosphate (NaPF ₆ ) is added to a solvent in which propylene carbonate (PC) and ethylene carbonate (EC) are mixed.

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