KR101771295B1 - Electrolyte solution for lithium metal battery and lithium metal battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte solution for a lithium metal battery and a lithium metal battery including the electrolyte solution. The electrolyte solution according to the present invention allows a more stable solid electrolyte interface (SEI) layer to be formed on the lithium electrode, thereby enabling the development of a more improved charging / discharging efficiency. Furthermore, the electrolyte solution according to the present invention can suppress the short circuit of the battery by suppressing the growth of lithium dendrite on the lithium electrode.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrolyte solution for a lithium metal battery, and a lithium metal battery including the electrolyte solution. BACKGROUND OF THE INVENTION [0002]

The present invention relates to an electrolyte solution for a lithium metal battery and a lithium metal 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 these secondary batteries, a battery using lithium as a negative electrode is referred to as a lithium metal battery.

When the lithium metal battery is driven, lithium ions are reduced on the surface of the lithium electrode. Depending on the combination of the solvent and the lithium salt forming the electrolyte solution, SEI (solid electrolyte interface) layers of various compositions are formed on the surface of the lithium electrode and irreversible .

However, if the SEI layer formed on the surface of the lithium electrode is unstable, the direct reaction between the electrolyte solution and the lithium electrode is continuously generated to cause additional irreversibility, which is associated with a decrease in the charge / discharge efficiency of the battery. In addition, formation of an unstable SEI layer causes depletion of the electrolyte solution and acts as a factor to lower the lifetime of the back cell, such as a gas being generated as a by-product.

As the lithium metal battery continues to be charged and discharged, a lithium dendrite having a large specific surface area is formed on the surface of the lithium electrode. However, when the lithium dendrite is grown on the lithium electrode, not only the safety of the battery is adversely affected, but also the corrosion of the electrode due to oxygen is accelerated.

The present invention provides an electrolyte solution for a lithium metal battery capable of inhibiting the growth of lithium dendrites while allowing formation of a more stable SEI layer on the lithium electrode.

And, the present invention is to provide a lithium metal battery including such an electrolyte solution.

According to the present invention,

Non-aqueous organic solvents;

_{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 At least one lithium salt selected from the group consisting of Li ₂ (SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (SFO ₂ ) ₂ and LiN (CF ₃ CF ₂ SO ₂ ) ₂ ; And

Additives including lithium polysulfide and lithium nitrate

An electrolyte solution for a lithium metal battery is provided.

According to the present invention, there is provided a lithium metal 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, a non-aqueous organic solvent; _{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 At least one lithium salt selected from the group consisting of Li ₂ (SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (SFO ₂ ) ₂ and LiN (CF ₃ CF ₂ SO ₂ ) ₂ ; And an electrolyte solution for a lithium metal battery comprising an additive including lithium polysulfide and lithium nitrate.

As a result of continuous experiments conducted by the present inventors, it has been found that, when lithium polysulfide and lithium nitrate are added as an additive together with a lithium salt such as LiTFSI in an electrolyte solution for a lithium metal battery, a more stable SEI layer can be formed on the lithium electrode Thereby enabling the development of an improved charging / discharging efficiency. Furthermore, it has been confirmed that the electrolyte solution containing the additive suppresses the growth of lithium dendrites on the lithium electrode, thereby reducing the possibility of short circuiting of the battery, thereby further improving the lifetime of the battery. The effect of applying an electrolyte solution containing lithium polysulfide and lithium nitrate as an additive to a lithium metal battery is significantly different from that of a lithium metal battery using a non-sulfur based anode containing no sulfur in the anode .

The effect of applying an electrolyte solution containing lithium polysulfide and lithium nitrate as an additive to a lithium metal battery is more remarkable than that of a lithium metal battery using a non-sulfur based anode containing no sulfur in the anode .

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 and cyclic ethers.

Preferably, the non-aqueous organic solvent includes a non-cyclic ether and a cyclic ether in a ratio of 1: 0.3 to 1: 0.7, or 1: 0.4 to 1: 0.7, or 1: 0.4 to 1: 0.6, May be advantageous in terms of improvement of the over-voltage phenomenon upon charging and development of an improved energy density. Here, the volume ratio corresponds to the ratio of "volume% of acyclic ether": "volume% of cyclic ether" in the ether solvent.

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, and tetraethylene glycol diethyl ether may be used alone or in combination.

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 metal 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, an electrolyte solution according to an embodiment of the present invention includes an additive dispersed in the non-aqueous organic solvent together with the lithium salt described above. Particularly, the additives include lithium polysulfide and lithium nitrate.

According to an embodiment of the present invention, an electrolyte solution containing lithium polysulfide and lithium nitrate as an additive forms a more stable solid electrolyte interface (SEI) layer on a lithium electrode than an electrolyte solution containing no such additive So that the charging and discharging efficiency can be further improved. Furthermore, the electrolyte solution suppresses the growth of lithium dendrite on the lithium electrode, thereby reducing the possibility of short circuit of the battery, thereby improving the lifetime of the battery.

As the lithium polysulfide in the additive, at least one compound selected from the group consisting of Li ₂ S ₂ , Li ₂ S ₄ , Li ₂ S ₆ , Li ₂ S ₈ , Li ₂ S ₁₀ , and Li ₂ S ₁₂ may be used have.

According to an embodiment of the present invention, the concentration ratio between lithium polysulfide and lithium nitrate contained in the electrolyte solution is not particularly limited.

However, it is preferable that the concentration of the additive contained in the electrolyte solution is controlled 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 additive contained in the electrolyte solution is preferably 0.01 M or more so that the effect of improving the performance of the battery due to the addition of the additive can be sufficiently manifested. 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. Therefore, the concentration of the additive is preferably 1.0 M or less.

II . The lithium metal battery including the electrolyte solution

On the other hand, according to another embodiment of the invention, there is provided a lithium metal battery comprising the above-described electrolyte solution.

The electrolyte solution can be applied to various lithium metal batteries using lithium metal as a cathode. Particularly, the effect of applying the electrolyte solution to a lithium metal battery may be significantly different from that of a lithium metal battery using a non-sulfur based anode in which the anode contains no sulfur.

The lithium metal battery includes a case, an electrode assembly disposed inside the case, including an anode and a cathode, and a separator interposed between the anode and the cathode, and the electrolyte solution injected into the case.

The lithium metal battery uses the lithium metal as a negative electrode, and any anode conventionally used can be used if the positive electrode is a non-sulfur based positive electrode.

Specifically, the positive electrode is prepared by preparing a composition for forming a positive electrode active material layer by mixing a positive electrode active material, a conductive agent, and a binder, applying the composition for forming the positive electrode active material layer to a positive current collector such as aluminum foil, .

As the positive electrode active material, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b < 1, 0 <c <1, a + b + c = 1), LiNi 1 - y Co y O 2, LiCo 1-y Mn y O 2, LiNi 1 -y Mn y O 2 (O≤y <1) _{, Li (Ni a Co b Mn} c) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2-z Ni z O 4, LiMn _{2- z} Co _z O ₄ (0 <z <2), LiCoPO ₄ and LiFePO ₄ , or a mixture of two or more thereof. In addition to these oxides, selenide and halide may be used.

The binder serves to attach the electrode active material particles to each other and to adhere the electrode active material to the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC) , Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber , Fluorine rubber, various copolymers thereof, and the like.

In addition, preferred examples of the solvent include dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP), acetone or water.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

The current collector may be any metal selected from the group consisting of copper, aluminum, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be carbon, nickel, The aluminum alloy may be an aluminum-cadmium alloy. Alternatively, a non-conductive polymer surface-treated with a conductive material, a conductive polymer, or the like may be used.

The collector may be coated with the composition for forming a cathode active material layer by a known method or by a suitable method in consideration of the characteristics of the material. For example, it is preferable that the composition for forming a cathode active material layer is dispersed on a current collector and then uniformly dispersed using a doctor blade or the like. In some cases, a method of performing the distribution and dispersion processes in a single process may be used. In addition, methods such as die casting, comma coating, and screen printing may be used.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer The porous polymer film made of a polymer may be used alone or in a laminated form, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, polyethylene terephthalate fiber or the like may be used. no.

As another example, the electrolyte solution can be preferably applied to a lithium-air battery.

A lithium-air battery is a battery system using lithium as a cathode and oxygen in the air as an active material of an anode (air electrode), and has a large energy density in addition to a lithium-sulfur battery. Because the oxygen in the air is supplied unlimitedly, it can store a large amount of energy through the air electrode having a large specific surface area.

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 at the cathode and reduction and oxidation of oxygen introduced from the outside occur at the cathode. 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.

In the lithium-air battery, depending on the type of the electrolyte solution, the kinds of ions migrating through the electrolyte solution are changed, and the kind of the reaction byproduct and the operating voltage may be changed.

According to an embodiment of the present invention, the cathode and the cathode of the lithium-air battery may have a conventional material and structure. For example, lithium metal or an alloy may be used as the cathode. As the air electrode, a slurry containing carbon black and a composite metal oxide catalyst may be coated on a porous current collector such as a nickel foam. As the electrolyte, an electrolyte solution containing the above-mentioned non-aqueous organic solvent, a lithium salt, and an additive may be used.

The electrolyte solution according to the present invention allows a more stable solid electrolyte interface (SEI) layer to be formed on the lithium electrode, thereby enabling the development of a more improved charging / discharging efficiency. Furthermore, the electrolyte solution according to the present invention can suppress the short circuit of the battery by suppressing the growth of lithium dendrite on the lithium electrode.

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

Lithium foil having a thickness of 150 mu m was prepared as a cathode, and a polyethylene film having a thickness of 16 mu m was prepared as a separator.

Then, to an ether solvent containing 1,2-dimethoxyethane (DME): tetraethylene glycol dimethyl ether (TEGDME): 1,3-dioxolane (DOL) in a volume ratio of 1: 1: 1, , 1.0 M of LiN (CF ₃ SO ₂ ) ₂ was added, and 0.05 M of Li ₂ S ₆ and 0.1 M of LiNO ₃ were added 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 metal battery.

Example  2

In Example 1, an ether solvent containing 1,2-dimethoxyethane (DME): tetraethylene glycol dimethyl ether (TEGDME): 1,3-dioxolane (DOL) in a volume ratio of 1: 1: Except that 1.0 M LiN (CF ₃ SO ₂ ) ₂ was added as a lithium salt and 0.5 M Li ₂ S ₆ and 0.1 M LiNO ₃ were added as an additive to prepare an electrolytic solution. To prepare a lithium metal battery.

Comparative Example  One

A lithium metal battery was prepared in the same manner as in Example 1, except that an electrolyte solution not containing Li ₂ S ₆ and LiNO ₃ as additives was used.

Comparative Example  2

A lithium metal battery was prepared in the same manner as in Example 1 except that an electrolyte solution not containing Li ₂ S ₆ was used as an additive.

Test Example : Lithium symmetric cell Of lithium metal

The initial efficiency (the ratio of the discharge capacity to the initial charge capacity) and the 15-cycle efficiency (the ratio of the discharge capacity to the 15th cycle charge capacity) were measured for each lithium metal cell according to Examples and Comparative Examples, The results are shown in Table 1 below.

Initial efficiency (%) 15 cycle efficiency (%) Example 1 91.91 88.10 Example 2 87.41 92.12 Comparative Example 1 Not measurable Not measurable Comparative Example 2 82.18 85.38

In the above experiment, the voltage was unstable due to the formation of an unstable passivation layer in Comparative Example 1, and calculation of the efficiency was impossible.

As can be seen from the above Table 1, the lithium metal batteries manufactured in Examples 1 and 2 have superior initial efficiency and 15 cycle efficiency as compared with the lithium metal battery prepared in Comparative Example 2, In the case of the lithium metal battery prepared in Examples 1 and 2, Li ₂ S ₆ and LiNO ₃ were added together to form a more stable SEI layer on the lithium electrode, thereby improving the charging / discharging efficiency, and lithium dendrite This is because the growth of the battery is suppressed and the life of the battery is improved as the possibility of short circuit of the battery is lowered.

Claims (8)

1. An electrolyte solution for a lithium metal battery comprising a non-spermacetate anode,
The electrolyte solution
Non-aqueous organic solvents;
_{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 At least one lithium salt selected from the group consisting of Li ₂ (SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (SFO ₂ ) ₂ and LiN (CF ₃ CF ₂ SO ₂ ) ₂ ; And
Additives including lithium polysulfide and lithium nitrate
And an electrolyte solution for a lithium metal battery. delete The method according to claim 1,
Wherein the concentration of the lithium salt is 0.2 to 2.0 M, and the concentration of the additive is 0.01 to 1.0 M. The method according to claim 1,
Wherein the lithium polysulfide is at least one compound selected from the group consisting of Li ₂ S ₂ , Li ₂ S ₄ , Li ₂ S ₆ , Li ₂ S ₈ , Li ₂ S ₁₀ , and Li ₂ S ₁₂ . solution. The method according to claim 1,
Wherein the non-aqueous organic solvent comprises acyclic ethers and cyclic ethers in a volume ratio of 1: 0.3 to 1: 0.7. The method according to claim 1,
Wherein the non-aqueous organic solvent comprises acyclic ethers and cyclic ethers in a volume ratio of 1: 0.4 to 1: 0.7. 6. The method of claim 5,
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 metal battery, which is the above compound. A lithium metal battery comprising the electrolyte solution according to claim 1 and a non-slurry anode.