KR20160050221A - Electrolyte solution for lithium-air battery and lithium-ion battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte solution for a lithium-air battery and a lithium-air battery including the same. According to the present invention, the electrolyte solution enables control of the shape of Li2O2 extracted as a result of discharge of a lithium-air battery and realization of an improved charging/discharging efficiency. Furthermore, according to the present invention, the electrolyte solution can suppress oxidation of the cathode of the lithium-air battery and growth of lithium dendrite in the anode, thereby reducing the possibility of a short circuit.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrolyte solution for a lithium-air battery, and a lithium-

The present invention relates to an electrolyte solution for a lithium-air battery and a lithium-air battery including the electrolyte solution.

BACKGROUND ART [0002] With the recent rapid development in the fields of electronic devices and electric vehicles, there is a growing demand for secondary batteries having a high energy density. Among such secondary batteries, a battery using lithium as a negative electrode is referred to as a lithium ion battery. Among them, a lithium-air battery is considered to be an excellent battery system in terms of electric capacity.

A lithium-air battery is a battery system that uses lithium as a cathode and oxygen in the air as an active material of an anode (air electrode). Since the lithium-air battery can receive unlimited supply of oxygen in the air, a large amount of energy can be stored through the air electrode having a large specific surface area. The lithium-air battery is advantageous in that it is smaller in size and lighter than other batteries because it does not need to mount a cathode active material.

Such a lithium-air battery can be said to be a battery system in which a secondary battery and a fuel cell technology are combined, in which oxidation and reduction of lithium occur in the cathode, and reduction and oxidation of oxygen introduced from the outside take place in the air electrode. In the lithium-air battery, during the discharge reaction, lithium ions and electrons are generated by the oxidation reaction of the lithium metal, and lithium ions move through the electrolyte solution, and electrons move to the air electrode along the external leads. The oxygen contained in the outside air flows into the air electrode and is reduced by the electrons moved along the conductor to form Li ₂ O ₂ . The charge reaction proceeds in the opposite way.

The resulting Li ₂ O ₂ in the lithium-air battery is hardly soluble in common electrolytes, and forms toroid-shaped particles on the surface of the air electrode. The Li ₂ O ₂ thus stacked covers the catalyst of the air electrode and causes poisoning. In addition, since Li ₂ O ₂ is an insulator having an extremely low electrical conductivity, the impedance of the air electrode is increased as the discharge progresses, and the charge and discharge efficiency is lowered.

Also, the cathode of the lithium-air battery continuously generates corrosion due to dissolved oxygen, superoxide, peroxide, etc. existing in the electrolyte solution. Further, as the charging and discharging are continued, a lithium dendrite having a large specific surface area is formed on the surface of the negative electrode. However, when the lithium dendrite is grown on the lithium electrode, there is a problem that not only the safety of the battery is adversely affected but also the corrosion of the cathode by oxygen is accelerated.

An object of the present invention is to provide an electrolyte solution for a lithium-air battery capable of suppressing the deterioration of the battery performance due to Li ₂ O ₂ as a result of discharge and suppressing the oxidation of the cathode and the growth of lithium dendrites in the anode.

The present invention is to provide a lithium-air battery including such an electrolyte solution with improved charging / discharging efficiency.

According to the present invention, there is provided an electrolyte solution for a lithium-air battery comprising a non-aqueous organic solvent, a lithium salt, and a metal-halide-based additive.

According to the present invention, there is provided a lithium-air battery including the electrolyte solution.

Hereinafter, an electrolyte solution and a lithium ion precursor according to embodiments of the present invention will be described in detail.

Prior to that, and unless explicitly stated throughout the present specification, the terminology is used merely to refer to a specific embodiment and is not intended to limit the present invention. And, the singular forms used herein include plural forms unless the phrases expressly have the opposite meaning. Also, as used herein, the term " comprises " embodies certain features, areas, integers, steps, operations, elements and / or components, It does not exclude the existence or addition of a group.

I. Electrolyte solution

According to one embodiment of the invention, there is provided an electrolyte solution for a lithium-air battery comprising a non-aqueous organic solvent, a lithium salt, and a metal-halide additive.

As a result of continuous experiments conducted by the present inventors, it has been confirmed that, when a metal-halide compound is added to an electrolyte solution for a lithium-air battery together with a lithium salt such as LiTFSI, the charge / discharge overvoltage can be remarkably improved. Particularly, it is expected that the improvement of the performance of the lithium-air battery by using the metal-halide additive is due to the fact that the shape of Li ₂ O ₂ precipitated from the cathode is controlled by the metal-halide additive.

In this connection, it has been reported that Li ₂ O _{2, which} is a discharge result in a lithium-air battery, is hardly dissolved in a general electrolyte and is formed as toroid-shaped particles on the surface of an air electrode. However, when an electrolyte solution containing a metal-halide-based compound is applied to a lithium-air battery as in an embodiment of the present invention, Li ₂ O ₂ differs from a general toroid shape by the action of a metal- Shaped. ≪ / RTI > For example, FIG. 2 is an enlarged view of an air electrode of a lithium-air battery to which an electrolyte solution according to an embodiment of the present invention is applied. It is confirmed that Li ₂ O ₂ is formed into a thin piece (flake) have.

As the shape of the discharge result is controlled by the metal-halide-based additive, it is expected that Li ₂ O ₂ deposited on the air electrode is more easily decomposed and the occurrence of the overvoltage upon charging is reduced. This effect can be ascertained through a control example that does not include a metal-halide additive.

Furthermore, the electrolyte solution containing the metal-halide additive suppresses the oxidation of the cathode in the lithium-air battery and suppresses the growth of lithium dendrite in the anode, thereby reducing the possibility of short circuit of the battery, - It is possible to improve the overall performance of the air battery.

In the electrolyte solution, a non-aqueous organic solvent is a medium through which ions involved in an electrochemical reaction of a battery can move.

According to an embodiment of the present invention, at least one ether-based solvent may be used as the non-aqueous organic solvent. Here, the ether solvent includes acyclic ethers or cyclic ethers.

Non-limiting examples of such non-cyclic ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane (1, 2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, dimethyl sulfoxide and N, N-dimethyl acetamide. And at least one compound selected from the group consisting of

Also, as non-limiting examples, the cyclic ethers may be 1,3-dioxolane, 4,5-dimethyl-dioxolane, Ethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, tetrahydrofuran, 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydrofuran, 2-ethoxy tetrahydrofuran, 2-methoxy-1,3-dioxolane, 2,5-dimethoxy tetrahydrofuran, dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl -1,3-dioxolane, tetrahydropyran, 1,4-dioxane, 1,2-dimethoxane, Benzene, 1,2-dimethoxy benzene, 1,3-dimethoxy benzene, 1,4-dimethoxy benzene, and isosorbide dimethyl ether) may be used.

Meanwhile, the electrolyte solution according to an embodiment of the present invention includes a lithium salt dispersed in the non-aqueous organic solvent.

As the lithium salt, those generally applicable to a lithium-air battery can be used without any particular limitation. Preferably, the lithium salt is _{LiSCN, LiBr, LiI, LiPF 6} , LiBF 4, LiSbF 6, LiAsF 6, LiCH 3 SO 3, LiCF 3 SO 3, LiClO 4, Li (Ph) 4, LiC (CF 3 SO _{2) 3, LiN (CF 3} SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiN (SFO 2) 2, and _{LiN (CF 3 CF 2 SO 2} ) at least one member selected from the group consisting of ₂ Lt; / RTI >

The concentration of the lithium salt may be determined in consideration of ionic conductivity and the like, preferably 0.2 to 2.0 M, or 0.5 to 1.6 M. That is, the concentration of the lithium salt is preferably 0.2 M or more in order to secure ion conductivity suitable for driving the battery. However, when the lithium salt is added in an excessive amount, the viscosity of the electrolyte solution may be increased to lower the mobility of the lithium ion, and the decomposition reaction of the lithium salt itself may increase, thereby deteriorating the performance of the battery. Therefore, the concentration of the lithium salt is preferably 2.0 M or less.

Meanwhile, the electrolyte solution according to an embodiment of the present invention includes the metal-halide-based additive dispersed on the non-aqueous organic solvent together with the lithium salt described above.

As the metal-halide additive, a metal chloride, a metal bromide, or a metal iodide may be used. In addition, in order to exhibit a more improved effect, the metal-halide additive is preferably a divalent or higher metal compound.

According to an embodiment of the present invention, the metal-halide additive is at least one compound selected from the group consisting of magnesium chloride (MgCl ₂ ), magnesium bromide (MgBr ₂ ), and magnesium iodide (MgI ₂ ) It is possible to more advantageously act on the expression of the effect.

The concentration of the metal halide-based additive contained in the electrolyte solution is preferably adjusted to 0.01 to 1.0 M, or 0.05 to 1.0 M, or 0.1 to 1.0 M, or 0.1 to 0.5 M. That is, the concentration of the metal-halide-based additive contained in the electrolyte solution is preferably 0.01 M or more so that the performance improvement effect of the battery due to the addition of the metal-halide-based additive can be sufficiently exhibited. However, when the additive is added in an excessive amount, the viscosity of the electrolyte solution may increase and the mobility of the lithium ion may be lowered, and the performance of the battery may be deteriorated. Accordingly, the concentration of the metal-halide-based additive is preferably 1.0 M or less.

II . The lithium-air battery including the electrolyte solution

According to another embodiment of the present invention, there is provided a lithium-air battery including the electrolyte solution described above.

That is, the lithium-air battery includes an electrolyte for a lithium-air battery including a non-aqueous organic solvent, a lithium salt, and a metal-halide additive.

According to an embodiment of the present invention, the lithium-air battery may have a conventional structure. The lithium-air battery includes a positive electrode (air electrode), which is a porous current collector carrying a negative electrode or a composite metal oxide catalyst, which is lithium metal or lithium alloy, and an electrolyte solution described between the negative electrode and the positive electrode.

Here, the air electrode may contain a composite metal oxide in an amount of 5 to 15% by weight based on the weight of the air electrode, and a conductive agent or a binder may be used if necessary. The material of the porous current collector carrying the composite metal oxide may be aluminum, nickel, iron, titanium, or the like.

Between the negative electrode and the air electrode, a separator impregnated with the above-described electrolyte solution may be provided. As the separator, a porous film such as polyethylene or polypropylene or a nonwoven fabric may be used.

The battery case for storing the negative electrode, the air electrode, and the electrolyte solution may be a case of a conventional shape such as a coin type, a flat plate type, a cylindrical type, or a laminate type.

The electrolyte solution according to the present invention enables control of the shape of Li ₂ O ₂ precipitated as a result of discharge of the lithium-air battery, thereby enabling the development of more improved charging / discharging efficiency. Further, the electrolyte solution according to the present invention not only can suppress the oxidation of the cathode in the lithium-air battery but also inhibits the growth of the lithium dendrite in the anode, thereby reducing the possibility of short circuit of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing changes in voltage versus charge and discharge capacity of a lithium-air battery according to an embodiment of the present invention and a comparative example. FIG.
2 is an enlarged view of the surface of an air electrode in a lithium-air battery according to an embodiment of the invention and a comparative example.

 BRIEF DESCRIPTION OF THE DRAWINGS Fig. However, the following embodiments are intended to illustrate the invention, but the invention is not limited thereto.

Example  One

Activated carbon was prepared as an air electrode for a lithium-air battery. The binder was applied with PTFE, and the electrode was prepared with a weight ratio of activated carbon to binder of 8: 2. The electrode was pressed to a thickness of 200 μm and vacuum dried at 120 ° C. for 12 hours. The prepared electrode was used as an electrode by tapping with a diameter of 19 phi. Lithium foil with a thickness of 150 μm was used as a negative electrode, and glass fiber was used as a separator with 19 phi.

Then, 1.0 M of LiN (CF ₃ SO ₂ ) ₂ was added as a lithium salt to tetraethylene glycol dimethyl ether (TEGDME) as an ether solvent, and 450 ppm of MgCl ₂ was added as an additive to prepare an electrolyte solution.

A separator was interposed between the prepared anode and cathode, and the electrolyte solution was injected into the battery case to prepare a lithium-air battery.

Comparative Example  One

A lithium-air battery was produced in the same manner as in Example 1, except that an electrolyte solution not containing MgCl ₂ as an additive was used.

Test Example  One

Each lithium-air cell according to Examples and Comparative Examples was subjected to a current density of 0.1 mA / cm < ² > to check the charge / discharge performance of the battery, and the voltage range was measured at 2.0 to 4.5V.

Referring to FIG. 1, the capacity of the battery was normalized in order to compare the effects of the precise electrolyte additive. The battery of Example 1 did not cause a significant change in discharge overvoltage as compared with the battery of Comparative Example 1, , It was confirmed that the overvoltage decreases more than 0.5V at the initial charge. In the case of the comparative example, it can be seen that the charging capacity when the upper limit voltage of 4.5 V is reached is relatively small, whereas the charging capacity is three times that of the comparative example. In addition, it can be seen that charging over-voltage is consistently lower than that of the comparative example in the charging process. It is thought that this not only improves the capacity of the electrode but also affects cycle life.

Test Example  2

After separating the air electrode from each lithium-air cell according to Example 1 and Comparative Example 1 used in Test Example 1, the residue remaining on the electrode was washed with DMC, and the surface of the air electrode was observed with a scanning electron microscope And the results are shown in Fig. In Fig. 1, the image of (a) is the surface of the air electrode separated from the cell of Example 1, and the image of (b) is the surface of the air electrode separated from the battery of Comparative Example 1. Fig.

As can be seen through the second, in the case of the comparative example As presented in the literature can be seen that the Li ₂ O _2, the discharge reaction of the toroid generated, which electrical pathway in accordance with the formed thicker the Li ₂ O _2, the non-conductive material It is known that overvoltage takes a great deal during the charging reaction in which decomposition occurs. As shown in FIG. 1, it is judged that the overvoltage is observed at the beginning of charging. However, in the case of the embodiment, since the shape of the reactant is formed not as a toroid but as a thin flake shape, it is considered that the electric pathway can be connected more smoothly than the thick toroid, and it is expected that the overvoltage upon charging is reduced. This can be deduced from the results shown in FIG. 1, and it was confirmed that by applying the electrolyte additive, it is possible to control the shape of the discharge and to improve the performance such as the reduction of the overvoltage and the cycle life.

Claims (9)

An electrolyte solution for a lithium-air battery, comprising a non-aqueous organic solvent, a lithium salt, and a metal-halide additive. The method according to claim 1,
The metal-halide additive is at least one compound selected from the group consisting of magnesium chloride (MgCl ₂ ), magnesium bromide (MgBr ₂ ), and magnesium iodide (MgI ₂ ). The method according to claim 1,
Wherein the metal-halide-based additive is contained in a concentration of 0.01 to 1.0 M. The method according to claim 1,
The lithium salt is _{LiSCN, LiBr, LiI, LiPF 6} , LiBF 4, LiSbF 6, LiAsF 6, LiCH 3 SO 3, LiCF 3 SO 3, LiClO 4, Li (Ph) 4, LiC (CF 3 SO 2) 3, _{LiN (CF 3 SO 2) 2} , LiN (C 2 F 5 SO 2) 2, LiN (SFO 2) 2, and _{LiN (CF 3 CF 2 SO 2} ) in a lithium least one compound selected from the group consisting of ₂ - Electrolyte solution for air cells. The method according to claim 1,
Wherein the lithium salt is contained at a concentration of 0.2 to 2.0 M. The method according to claim 1,
Wherein the non-aqueous organic solvent is a non-cyclic ether or a cyclic ether. The method according to claim 6,
The non-cyclic ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, Diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, diethylene glycol dimethyl ether, (1) selected from the group consisting of tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, dimethyl sulfoxide and N, N-dimethyl acetamide. An electrolyte solution for a lithium-air battery. The method according to claim 6,
The cyclic ethers include 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane (4 , 5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, dioxolane, tetrahydrofuran, 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxy tetrahydrofuran, 2-methoxy-1, 3-dioxolane, 2-vinyl- 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, Tetrahydropyran, 1,4-dioxane, 1,2-dimethoxybenzene, 1,2-dimethoxybenzene, One selected from the group consisting of 1,3-dimethoxy benzene, 1,4-dimethoxy benzene, and isosorbide dimethyl ether. An electrolyte solution for a lithium-air battery, which is the above compound. A lithium-air battery comprising the electrolyte solution according to claim 1.

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