KR20160063773A - The sodium rechargeable battery - Google Patents

Abstract

Provided is a sodium rechargeable battery, comprising: a positive electrode which includes a positive electrode material adapted to store sodium ions during discharging; a negative electrode which includes a graphite negative electrode material adapted to store the sodium ions during charging; a separator which transfers the sodium ions between the positive electrode and the negative electrode; and an ether-based electrolyte which can use the sodium ions in the positive electrode and the negative electrode as transfer media, and includes sodium salt, wherein a voltage at which the sodium ions are stored can be adjusted according to the type of ether-based electrolyte. According to an embodiment of the present invention, a graphite material can be used as a negative electrode material of a sodium secondary battery; desirable cycle and charging/discharging rate characteristics can be achieved; and combination with various positive electrode materials can be achieved.

Description

The sodium rechargeable battery

The present invention relates to a sodium secondary battery, and more particularly, to a sodium secondary battery using an ether-based electrolyte.

As the market share of lithium-ion batteries in the energy storage industry increases, the price of lithium, a rare material, will increase. There is a great deal of interest in the development of ion batteries based on sodium, which is distributed throughout the world compared to lithium. In addition, as renewable energy for the realization of low-carbon society emerged, the development of high-performance accumulators became important. Lithium-ion batteries with small and light weight and high energy density are playing a role, but it is required to reduce the cost of the batteries in order to supply them to large-capacity residential batteries.

Therefore, for the purpose of cost reduction, a battery using a large amount of sodium is relatively advantageous than a battery using lithium. However, sodium ion battery is more concerned about safety than lithium ion battery, and sodium is difficult to handle because it is chemically activated well.

In addition, graphite is widely used in lithium ion batteries because of its excellent energy storage characteristics, but it is known that graphite can not be used as a negative electrode material of a sodium secondary battery. Up to now, there has been a problem in that insertion and desorption of reversible sodium do not occur when the graphite cathode is used in a sodium secondary battery.

Korean Patent Publication No. 10-2003-0052949 (Jun. 27, 2003)

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a sodium secondary battery which can be used as an anode material of a sodium secondary battery. However, these problems are exemplary and do not limit the scope of the present invention.

According to an aspect of the present invention, a sodium secondary battery includes: a cathode having a cathode material for storing sodium ions when discharging; An anode having a graphite anode material for storing the sodium ion when charged; A separation membrane for transferring the sodium ions between the anode and the cathode; And an ether-based electrolyte capable of using the sodium ion as a transfer medium to the anode and the cathode, the sodium-based electrolyte having a sodium salt, Can be controlled.

The ether-based electrolyte may include at least one of diethylene glycol dimethyl ether (DEGDME), tetraethylene glycol dimethyl ether (TEGDME), and dimethyl cetyl ether (Dimethoxyethane, glyme) have.

The longer the chain length of the ether-based electrolyte is, the higher the voltage for storing the sodium ion can be.

The cathode material may include a sodium metal compound.

The separator may comprise polyethylene (PE) or polypropylene (PP).

According to one embodiment of the present invention as described above, when the ether-based electrolyte is used, the graphite material can be used as an anode material of a sodium secondary battery, and excellent cycling characteristics and high charge / And can be combined with a sodium anode material of various transition metal compounds to realize a sodium secondary battery pull cell having excellent characteristics. Of course, the scope of the present invention is not limited by these effects.

1 is a schematic view illustrating a structure of a sodium secondary battery according to an embodiment of the present invention.
FIG. 2 is a flowchart schematically illustrating a method of manufacturing an ether-based electrolyte of a sodium secondary battery according to an embodiment of the present invention.
FIGS. 3 to 8 are graphs showing characteristics of a sodium secondary battery according to Experimental 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. It should be understood, however, that the invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, Is provided to fully inform the user. Also, for convenience of explanation, the components may be exaggerated or reduced in size.

Terms such as "top" or "bottom" referred to in the process of describing the present embodiment may be used to describe the relative relationship of certain elements to other elements, as illustrated in the figures. That is, relative terms may be understood to include different directions of the structure apart from the directions depicted in the figures. For example, if the top and bottom of the structure are inverted in the figures, the elements depicted as being on the top surface of the other elements may be on the bottom surface of the other elements. Thus, by way of example, the term "tops" may include both "top" and "bottom" directions, relative to a particular direction in the figures.

Further, in the course of describing the present embodiment, when it is mentioned that an element is located on another element, or "connected" to another element, the element is positioned directly on the other element Or directly connected to the other component, but may also mean that one or more intervening components may be present therebetween. However, when an element is referred to as being "directly on" another element, "directly connected" to another element, or "directly in contact" with another element, Which means that there are no intervening components.

In the following embodiments, the x-axis, the y-axis, and the z-axis are not limited to three axes on the orthogonal coordinate system, but can be interpreted in a broad sense including the three axes. For example, the x-axis, y-axis, and z-axis may be orthogonal to each other, but may refer to different directions that are not orthogonal to each other.

1 is a schematic view illustrating a structure of a sodium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, the structure of a sodium secondary battery 1 according to an embodiment of the present invention includes an anode 10 having a cathode material 12 for storing sodium ions 16 when discharged, A separator 30 for transferring sodium ions 16 between the anode 10 and the cathode 20 and a separator 30 for separating the anode 10 and the cathode 20 from each other, Sodium ions 30 may be used as a transfer medium in the cathode 20 and may include an ether-based electrolyte 40 having a sodium salt.

In more detail, the anode 10 is an electrode that receives electrons from an external conductor and reduces the cathode material 12. The positive electrode 10 is composed of a current collector 14 which collects electrons and sends them to external leads, and an active material 12 which has a structure capable of inserting and desorbing sodium ions 16. For example, the anode material 12 may comprise a sodium metal compound. The metal compound may be composed of oxygen ions 12a and metal ions 12b. The cathode 20 is an electrode for emitting electrons to the conductor while the anode material 22 is oxidized. The cathode 20 is made of an active material (anode material) 22 having a structure capable of inserting and removing a sodium ion 16 and a current collector 24, collecting electrons and collecting electrons as an anode 10, Lt; / RTI > For example, the anode material 22 may include graphite.

The electrolyte 40 is a medium in which mass transfer (migration of the sodium ions 16) occurs so that the reduction of the anode 10 or the oxidation reaction of the cathode 20 takes place in chemical harmony. The electrolyte 40 should have low viscosity (dissociation of the sodium salt is better as the dielectric constant is higher) (the lower the viscosity is, the easier the sodium ion 16 is to be delivered). For example, the electrolyte 40 may include at least one of diethylene glycol dimethyl ether (DEGDME), tetraethylene glycol dimethyl ether (TEGDME), and dimethyl cetyl ether . ≪ / RTI > The voltage for storing the sodium ions 16 can be controlled depending on the kind of the ether-based electrolyte 40. The longer the chain length of the ether-based electrolyte 40, the higher the voltage for storing the sodium ions 16 . The separator 30 is a separator for preventing physical contact between the anode 10 and the cathode 20. The separation membrane 30 has a fine pore structure so that the sodium ions 16 can move. For example, the separation membrane 30 may comprise polyethylene (PE) or polypropylene (PP).

In other words, the sodium secondary battery 1 is a device for converting the chemical energy of the internal active material into electrical energy by a chemical reaction. The sodium secondary battery (1) has a special internal structure to allow electrons to escape to the outside through an electrochemical reaction. Electrons flowing through the lead wire can provide electricity as a source of electric energy. Components of the sodium secondary battery 1 include a cathode 10 as an electrode to which the cathode active material 12 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 anode active material 22. [ ), An ether-based electrolyte 40 as a medium in which mass transfer occurs so that the reduction reaction and the oxidation reaction of the active material can achieve chemical harmony, and a separation membrane 30 for preventing physical contact between the anode 10 and the cathode 20 .

On the other hand, the cathode 20 of the sodium secondary battery 1 is a substance which gives off electrons and is oxidized. On the other hand, the anode 10 is a material which receives electrons (together with cations) and is reduced. When the sodium secondary battery 1 is connected to the external load 50 to perform a 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 move to the anode 10 via the external rod 50, cause a reduction reaction with the anode material 12, And in the ether-based electrolyte 40 by mass transfer of anions and cations in the direction of the anode 10.

FIG. 2 is a flowchart schematically illustrating a method of manufacturing an ether-based electrolyte of a sodium secondary battery according to an embodiment of the present invention.

Referring to FIG. 2, a method of preparing an ether-based electrolyte of a sodium secondary battery according to an embodiment of the present invention includes removing sodium (S100) water contained in a sodium salt (S100) (S200), and a step S300 of storing the electrolyte in the molecular sieve to control the moisture contained in the electrolyte.

Hereinafter, an experimental example to which the technical idea described above is applied will be described in order to facilitate understanding of the present invention. It should be understood, however, that the following examples are for the purpose of promoting understanding of the present invention and are not intended to limit the scope of the present invention.

[Experimental Example 1]

NaPF ₆ , NaClO ₄ , and NaCF ₃ SO ₃ , which are sodium salts, are stored in an oven at 180 ° C for 3 days to remove moisture. A sodium salt of 1 molar concentration is dissolved in ether-based electrolytes such as DEGDME, TEGDME, and DME. To control the moisture content of a 1-molar electrolyte, it is placed in a molecular sieve and stored for about 2 days to produce an ether-based electrolyte. A sodium secondary battery full cell was implemented using Na _1.5 VPO _4.8 F _0.7 as the anode, graphite as the cathode, and the ether-based electrolyte prepared.

[Experimental Example 2]

NaPF ₆ , NaClO ₄ , and NaCF ₃ SO ₃ , which are sodium salts, are stored in an oven at 180 ° C for 3 days to remove moisture. A sodium salt of 1 molar concentration is dissolved in ether-based electrolytes such as DEGDME, TEGDME, and DME. To control the moisture content of a 1-molar electrolyte, it is placed in a molecular sieve and stored for about 2 days to produce an ether-based electrolyte. Using a Na ₂ Mn _x Fe _3-x (PO ₄ ) ₂ (P ₂ O ₇ ) (x = 0, 1, 2, 3) as an anode, graphite as a cathode and an ether- We implemented a full cell cell.

[Comparative Example]

NaPF ₆ , NaClO ₄ , and NaCF ₃ SO ₃ , which are sodium salts, are stored in an oven at 180 ° C for 3 days to remove moisture. 1 Molar sodium salt is dissolved in DMC (dimethyl carbonate), EC (ethylene carbonate) / DEC (diethylene carbonate) or THF (Tetrahydroxyfuran) electrolytic solution. To control the moisture content of a 1-molar electrolyte, it is placed in a molecular sieve and stored for about 2 days to produce a carbonate-based electrolyte. A sodium secondary battery full cell was implemented using Na _1.5 VPO _4.8 F _0.7 as an anode, graphite as a cathode, and a carbonate-based electrolyte prepared.

3 to 8 are graphs showing the results of the characteristics of the sodium secondary battery according to Experimental Examples and Comparative Examples of the present invention.

Referring to FIG. 3, FIG. 3 is a cyclic voltammetry test result of the sodium secondary battery of the present invention. Cyclic voltametry is a method of obtaining current and potential curves at solid electrodes and the like, and periodically changes the electrode potential using a triangular wave. The oxidation or reduction behavior of the compound in the solution and the electrode material itself can be confirmed. 3 (a), when a carbonate-based electrolyte is used as in the comparative example, the graphite material shows no electrochemical reaction in the sodium secondary battery. On the other hand, as in Experimental Example 1, it can be seen that the oxidation / reduction current reversibly appears when an ether-based electrolyte is used. In addition, it can be seen that no reversible reaction occurs unless the sodium salt is added to the ether-based electrolyte.

Referring to FIGS. 3 (b) to 3 (e), when an ether-based electrolyte is used, a high operating voltage of about 150 mAh / g can be exhibited when a low operating voltage of about 0.6 V is exhibited. On the other hand, when a carbonate electrolyte is used, a very low capacity of about 70 mAh / g or less is obtained at the same operating voltage.

FIG. 4 is a graph showing the results of a charge and inversion cycle of a sodium secondary battery according to an experimental example of the present invention. Referring to FIG. 4 (a), when the ether-based electrolyte according to Experimental Example 1 is used, it can be seen that the graphite cathode proceeds without a large capacity decrease to about 2500 cycles or more. Also, referring to FIG. 4 (b), it can be seen that the capacity is maintained well even at a very high current speed.

FIG. 5 is a graph showing characteristics of a sodium secondary battery according to various experiments according to the present invention. FIG. Figure 5 (a) shows the electrochemical properties of graphite cathodes in various ether-based electrolytes. 5 (a), reversible sodium storage and desorption reactions can be confirmed in all of the ether-based electrolytes. Referring to FIG. 5 (b), it can be seen that the voltage for storing sodium can be adjusted from about 0.6 V to about 0.78 V according to the chain length of the electrolyte. 5 (c), each of the ether-based electrolytes exhibited excellent cycle characteristics, and FIG. 5 (d) shows that when the DEGDME electrolyte solution was used, Fast charge / discharge characteristics were the best.

6 is a TEM (Transmission Electron Microscope) result of a test step of a sodium secondary battery according to an experimental example of the present invention. 6 (a) to 6 (c), a graphical transmission electron microscope image of each stage was taken while a charge reversal cycle test of a sodium secondary battery was performed using an ether-based electrolyte as a graphite cathode. It can be seen that the interlayer spacing of the graphite after discharge increases to about 0.42 nm to 0.53 nm as compared with that before discharge of the sodium secondary battery, and at the same time, the well-aligned structure is broken between the graphite layers. After charging, the interlayer spacing is again returned to about 0.34 nm, and the structure becomes aligned. Through this, it can be seen that sodium is inserted and desorbed into the graphite.

6 (d) and 6 (e), a peak of sodium ion solvated in the ether-based electrolytic solution after discharge shows that the electrolytic solution and sodium ion are inserted together at the time of discharge . In addition, it is thermodynamically impossible for sodium ions to enter the graphite itself, but it is thermodynamically feasible for the sodium ions enclosed in the electrolyte to enter together.

7 is a filling curve of a sodium secondary battery according to an experimental example of the present invention. FIG. 7 (a) is a filling curve of Na _1.5 VPO _4.8 F _{0.7 which} is a cathode material of a sodium secondary battery, (b) is a charge / discharge curve of a sodium secondary battery full cell of Na _1.5 VPO _4.8 F _0.7 anode and graphite cathode using DEGDME as an ether-based electrolyte (1M NaPF ₆ in DEGDME), and FIG. 7 (c) (B) is a cycle test result of the full cell. 7C shows a capacity of about 45 mAh / g (considering both the anode and cathode weights) at a current rate of about 0.1 A / g and a capacity of about 18 mAh / g even at a high current rate of about 1 A / . ≪ / RTI > Also, it can be confirmed that charging and discharging are possible without reducing the capacity for about 250 cycles.

8 is a graph showing characteristics of a sodium secondary battery according to another experimental example of the present invention. 8 (a) to 8 (d) commonly use graphite as a negative electrode and various compositions of Na ₄ Mn _x Fe _3-x (PO ₄ ) ₂ (P ₂ O ₇ ) (x = 0, 1, 2, 3) as an anode and 1M NaPF ₆ in DEGDME ether-based electrolyte. Therefore, referring to FIGS. 7 and 8, when a graphite is used as a cathode and an ether-based electrolyte is used, a sodium secondary battery pull cell can be realized in combination with a sodium anode material of various transition metal compounds.

According to the above description, it is known that graphite, which is generally used as a negative electrode material of a lithium secondary battery, can not be used as a material for a sodium secondary battery up to now. Up to now, when graphite cathodes were used in sodium secondary batteries, no reversible sodium insertion or desorption occurred. In the present invention, when an ether-based electrolyte other than a carbonate-based electrolyte used as an electrolyte for a sodium secondary battery is used, the graphite material exhibits a very large activity and demonstrates reversible electrochemical reaction Respectively.

Therefore, it has been confirmed that energy can be stored through co-intercalation of sodium ions and an electrolyte when an ether-based electrolyte is used. An ether-based electrolyte can be used to develop a sodium secondary battery having graphite as a negative electrode and a transition metal compound as a positive electrode.

In addition, when an ether-based electrolyte is used, a sodium secondary battery exhibiting excellent cycling characteristics of about 2000 cycles or more and exhibiting excellent charge / discharge characteristics and exhibiting excellent characteristics when assembling a pull cell in combination with an anode of various materials can be realized .

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

1: Sodium secondary battery
10: anode
12: cathode material (cathode active material)
12a: oxygen ion
12b: metal ion
14: + the whole house
16: Sodium ion
20: cathode
22: anode material (anode active material)
24: - Whole house
30: Membrane
40: electrolyte
50: External load

Claims (5)

A cathode having a cathode material for storing sodium ions when discharged;
An anode having a graphite anode material for storing the sodium ion when charged;
A separation membrane for transferring the sodium ions between the anode and the cathode; And
An ether-based electrolyte capable of using the sodium ion as a transfer medium to the anode and the cathode, and having a sodium salt;
/ RTI >
And a controller for controlling the voltage for storing the sodium ion according to the type of the ether-
Sodium secondary battery. The method according to claim 1,
The ether-based electrolyte may include at least one selected from the group consisting of diethylene glycol dimethyl ether (DEGDME), tetraethylene glycol dimethyl ether (TEGDME), and dimethyl cetyl ether (Dimethoxyethane, glyme) Sodium secondary battery. The method according to claim 1,
Wherein the longer the chain length of the ether-based electrolyte is, the higher the voltage for storing the sodium ion is. The method according to claim 1,
Wherein the cathode material comprises a sodium metal compound. The method according to claim 1,
Wherein the separator comprises polyethylene (PE) or polypropylene (PP).

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