KR102045472B1 - Electrolytes for lithium metal secondary battery - Google Patents

Abstract

Lithium salts; Ether solvents; Fluorinated solvents; There is provided an electrolyte solution for a lithium metal secondary battery comprising an additive.

Description

Electrolyte for lithium metal secondary battery {Electrolytes for lithium metal secondary battery}

It relates to a lithium metal secondary battery electrolyte and a lithium metal secondary battery comprising the same.

Lithium metal has attracted attention as a cathode material for lithium secondary batteries with a high weight-per-weight capacity of 3,860 mAh / g and a low standard electrode potential (-3.04 V vs normal hydrogen electrode). However, lithium metal is very reactive and an extremely reducing atmosphere is formed during the charging process, resulting in an irreversible decomposition reaction between the lithium metal and the electrolyte. Decomposition reactions result in electrolyte depletion, and the decomposition products form non-uniform coatings on the lithium metal surface. In addition, as charging and discharging are repeated, lithium grows in a dendrite form. Such dendritic lithium causes an electrical short in the battery, leading to ignition of the battery, and thus causing a problem in safety.

Therefore, in order to apply a lithium metal having high stability and high capacity, it is necessary to develop an electrolyte solution to alleviate the reactivity of lithium metal, prevent dendritic lithium growth, and enable uniform lithium plating.

One aspect is to provide an electrolyte solution for a lithium metal secondary battery that effectively suppresses side reactions between lithium metal and an electrolyte solution, and at the same time suppresses dendritic lithium formation on a lithium metal surface.

According to one aspect, a lithium salt; Ether solvents; Fluorinated solvents; As an electrolyte solution for lithium metal secondary batteries containing an additive,

The ether solvent is selected from a glyme solvent,

The fluorinated solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3, tetrafluoropropylether, 1,1,2,2-tetrafluoroethyl-1H, 1H, 5H-octafluoropentyl ether, and combinations thereof,

The additive is selected from fluoroethylene carbonate, lithium difluoro (oxalato) borate, lithium difluorobis (oxalato) phosphate, and combinations thereof,

When the fluorinated solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3, tetrafluoropropylether, the additive is provided with an electrolyte solution for a lithium metal secondary battery, not fluoroethylene carbonate. .

In the present embodiment, the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiBOB, LiTFSI, LiFSI, LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (x, y is 1 to 20), LiCl, LiI or mixtures thereof Can be.

In this embodiment, the concentration of the lithium salt may be 2 M to 4 M.

In this embodiment, the glyme solvent may be 1,2-dimethoxyethane, 1,3-dioxolane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or a combination thereof.

In the present embodiment, the glymeic solvent may be included in 70% by volume to 90% by volume based on the total volume of the electrolyte.

In this embodiment, the fluorinated solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3, -tetrafluoropropylether, and the additive is lithium difluoro (oxalato). Borate, or a combination of fluoroethylene carbonate and lithium difluorobis (oxalato) phosphate.

In this embodiment, the fluorinated solvent is 1,1,2,2-tetrafluoroethyl-1H, 1H, 5H-octafluoropentyl ether, and the additive is fluoroethylene carbonate or lithium difluoro ( Oxalato) borate.

In this embodiment, the fluorinated solvent may be included in 10% by volume to 30% by volume based on the total volume of the electrolyte.

In the present embodiment, the volume ratio of the ether solvent and the fluorinated solvent may be 90:10 to 60:40.

In the present embodiment, the lithium metal secondary battery electrolyte may further include a linear carbonate solvent, a cyclic carbonate solvent, or a combination thereof.

In this embodiment, the linear carbonate-based solvent may include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, or a combination thereof.

In the present embodiment, the cyclic carbonate solvent may include ethylene carbonate, propylene carbonate, or a combination thereof.

In the present embodiment, the additive may be included 1 part by weight or more based on 100 parts by weight of the total electrolyte.

According to another aspect, an anode; A negative electrode comprising lithium metal; And it provides a lithium metal secondary battery comprising the above-mentioned electrolyte for lithium metal secondary battery.

Electrolyte according to one aspect includes a high concentration of lithium salt and fluorinated solvent, effectively suppresses side reactions of lithium metal and electrolyte, and at the same time reversibility of the plating and stripping reaction of lithium metal Maximized and suppressed dendritic lithium formation to improve battery stability.

1 (a) to 1 (b) are graphs showing changes in current according to voltage rise of coin cells manufactured in Example 1 and Comparative Examples 1 to 5. FIG.
2 (a) to 2 (b) are graphs showing charge and discharge cycle characteristics of the coin cells produced in Example 2 and Comparative Examples 6 to 12. FIG.
3 (a)-(f) are charge and discharge graphs of the coin cells produced in Examples 3 to 5 and Comparative Examples 13 to 18. FIG.
4 (a)-(b) are charge and discharge graphs of the coin cells produced in Example 6 and Comparative Examples 19 to 24. FIG.
5 is a schematic view of a lithium battery according to an exemplary embodiment.
<Explanation of symbols for the main parts of the drawings>
1: lithium battery 2: negative electrode
3: anode 4: separator
5: battery case 6: cap assembly

The present inventive concept described below may apply various transformations and have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all transformations, equivalents, or substitutes included in the technical scope of the present invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the inventive concepts. Singular expressions include plural expressions unless the context clearly indicates otherwise. Hereinafter, terms such as "comprise" or "have" are intended to indicate that there is a feature, number, step, action, component, part, component, material, or combination thereof described in the specification, one or the same. It is to be understood that the foregoing does not exclude in advance the possibility of the presence or addition of other features, numbers, steps, operations, components, parts, components, materials, or combinations thereof.

Hereinafter, the lithium metal secondary battery electrolyte and the lithium metal secondary battery employing the electrolyte according to exemplary embodiments will be described in more detail.

Lithium metal secondary battery electrolyte according to one aspect is a lithium salt; Ether solvents; Fluorinated solvents; It may include an additive.

The lithium metal secondary battery electrolyte includes a fluorinated solvent and an additive, thereby forming a stable SEI layer on the surface of the positive electrode and the negative electrode, not only suppressing side reactions with the electrolyte, but also suppressing the formation of a lithium metal resin phase on the surface of the battery. Improves stability.

According to one embodiment, the lithium salt can be used as long as it is a lithium salt generally used in the preparation of the electrolyte in the art. For example, the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiBOB, LiTFSI, LiFSI, LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (x, y is 1 to 20), LiCl, LiI or mixtures thereof have.

According to one embodiment, the concentration of the lithium salt may be 2 M to 4 M. For example, the concentration of the lithium salt may be 3 M to 4 M.

When the concentration of the lithium salt is in the above range, the frequency of contact of the solvent molecules in the electrolyte with the lithium salt is higher than the frequency of contact with the lithium metal anode, thereby reducing the reduction of the electrolyte at the surface of the lithium metal anode. Therefore, the precipitation of the product due to the reduction reaction of the electrolyte on the surface of the lithium metal negative electrode can be suppressed.

According to one embodiment, the ether solvent may be selected from a glyme solvent. The glymeic solvent is also expressed as a glycol ether, and since the dipole moment is high to improve lithium ion mobility and lithium salt dissociation, the electrolyte containing the same has excellent ion conductivity.

For example, the glymeic solvent may be 1,2-dimethoxyethane, 1,3-dioxolane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or a combination thereof, but is not limited thereto. Any glycol ethers are included.

According to one embodiment, the ether solvent may be included in 70% by volume to 90% by volume based on the total volume of the electrolyte. When the ether solvent is included in an amount within the above range, it is possible to sufficiently dissociate a high concentration of lithium salt and obtain excellent ionic conductivity.

According to one embodiment, the fluorinated solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3, -tetrafluoropropylether, 1,1,2,2-tetrafluoro Ethyl-1H, 1H, 5H-octafluoropentylether, and combinations thereof.

The electrolyte solution containing such a fluorinated solvent affects the flame retardancy and oxidation resistance of the electrolyte, and the fluorinated solvent forms an SEI film on the surface of the cathode, thereby suppressing further reduction of the cathode and the electrolyte composed of lithium metal, and Prevent oxidation.

The content of the fluorinated solvent may be included in 10% by volume to 30% by volume based on the total volume of the electrolyte. When the content of the fluorinated solvent falls within the above range, a stable SEI film is formed on the surface of the lithium metal negative electrode, thereby suppressing side reactions of the electrolyte solution, thereby suppressing the formation of a lithium metal resin phase on the surface of the lithium metal negative electrode, thereby improving stability of the battery. Not only is it significantly improved, but also has high energy density characteristics through suppression of loss of electrolyte solution.

According to one embodiment, the additive may be selected from fluoroethylene carbonate, lithium difluoro (oxalato) borate, and combinations thereof.

The additive may be included 1 part by weight or more based on 100 parts by weight of the total electrolyte. For example, the additive may include 1.5 parts by weight, 2 parts by weight, or 3 parts by weight or more based on 100 parts by weight of the total electrolyte, but is not limited thereto and does not impair battery characteristics of the lithium metal secondary battery. It can be used in an amount that does not range.

When the additive is added in excess, the viscosity of the electrolyte may increase. In particular, lithium difluoro (oxalato) borate can cause an increase in viscosity by increasing ionic interactions due to lithium ions. The high viscosity of the electrolyte solution acts as a resistance to the movement of lithium ions during charge and discharge, resulting in capacity reduction and deterioration of cycle characteristics. In this regard, lithium thifluoro (oxalato) borate containing lithium ions may be included in an amount of 6 parts by weight or less based on 100 parts by weight of the total electrolyte, but is not limited thereto and may be included in a range that does not deteriorate battery characteristics. have.

The additive may prevent oxidation of the electrolyte at the anode interface by forming an SEI film through an oxidation reaction in preference to other solvents in the electrolyte at the anode surface. This suppresses the loss of the electrolyte and improves the efficiency of the battery.

According to one embodiment, the fluorinated solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3, -tetrafluoropropylether and the additive is lithium difluoro (oxalato). ) Borate, or a combination of fluoroethylene carbonate and lithium difluorobis (oxalato) phosphate.

According to another embodiment, the fluorinated solvent is 1,1,2,2-tetrafluoroethyl-1H, 1H, 5H-octafluoropentylether, and the additive is fluoroethylene carbonate, or lithium difluoro (Oxalato) borate.

As described above, when using an electrolyte solution containing a specific combination of fluorinated solvents and additives, a stable SEI layer can be formed on the surface of the positive electrode and the negative electrode even at a high rate, thereby making it possible to manufacture a lithium metal secondary battery having high lifetime characteristics and high efficiency. Do.

According to one embodiment, the volume ratio of the ether solvent and the fluorinated solvent may be 90:10 to 60:40.

For example, the volume ratio of the ether solvent and the fluorinated solvent may be 80:20, but is not limited thereto.

According to one embodiment, the above-described lithium metal secondary battery electrolyte may further include an organic solvent having a low boiling point. The low boiling point organic solvent means a solvent having a boiling point of 200 ° C. or lower at 25 ° C. and 1 atmosphere.

The organic solvent may be selected from carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, aprotic solvents, and combinations thereof, but is not necessarily limited thereto and may be a low-boiling organic solvent that may be used in the art. Ramen is all possible.

Specifically, the carbonate-based organic solvent may include a linear carbonate-based solvent or a cyclic carbonate-based organic solvent.

For example, the linear carbonate solvent is dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (methyl propyl carbonate), ethyl propyl carbonate (ethyl propyl carbonate), diethyl Carbonate (diethyl carbonate, DEC), dipropyl carbonate (dipropyl carbonate), or a combination thereof.

For example, the cyclic carbonate solvent may include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, or a combination thereof.

The ester organic solvent may be methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (1,1 -dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), γ-butyrolacton (GBL), decanolide, valerian It may include one or more selected from the group consisting of rolactone (valerolactone), mevalonolactone, and caprolactone (caprolactone).

The ether organic solvent is dibutyl ether, tetraglyme (tetraethylene glycol dimethyl ether, TEGDME), diglyme (diethylene glycol dimethyl ether, DEGDME), dimethoxy ethane, 2-methyltetrahydro It may include one or more selected from the group consisting of furan (2-methyltetrahydrofuran), and tetrahydrofuran (tetrahydrofuran).

The ketone organic solvent may include cyclohexanone, the alcohol solvent may include ethyl alcohol, or isopropyl alcohol, and the aprotic solvent may be used. Nitrile dimethylformamide (dimethyl formamide, DMF), such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group and may include a double bond aromatic ring or ether bond) Amides, and dioxolanes such as 1,3-dioxolane may comprise one or more selected from the group consisting of sulfolanes (sulfolanes).

The organic solvent may be used alone or in combination of one or more, and the mixing ratio in the case of mixing one or more may be appropriately adjusted according to the desired battery performance, which is easy by those skilled in the art. Can be understood.

According to another aspect, an anode; A negative electrode comprising lithium metal; And it provides a lithium metal secondary battery comprising the above-mentioned electrolyte for lithium metal secondary battery. The lithium battery is not particularly limited in form, and includes a lithium secondary battery as well as a lithium primary battery such as a lithium ion battery, a lithium ion polymer battery, a lithium sulfur battery, and the like.

Lithium metal secondary battery according to one aspect may be manufactured by the following method.

First, the anode is prepared.

For example, a cathode active material composition in which a cathode active material, a conductive material, a binder, and a solvent are mixed is prepared. The cathode active material composition is directly coated on a metal current collector to prepare a cathode plate. Alternatively, the cathode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to prepare a cathode plate. The anode is not limited to the above enumerated forms and may be in any form other than the foregoing.

The positive electrode active material, in addition to the positive electrode active material described above, as a lithium-containing metal oxide, any one can be used without limitation as long as it is commonly used in the art. For example, one or more of a complex oxide of metal and lithium selected from cobalt, manganese, nickel, and combinations thereof may be used, and specific examples thereof include Li _a A _1-b B ¹ _b D ¹ ₂ (Wherein 0.90 ≦ a ≦ 1.8, and 0 ≦ b ≦ 0.5); Li _a E _1-b B ¹ _b O _2-c D ¹ _c (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); LiE _2-b B ¹ _b O _4-c D ¹ _c (wherein 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li _a Ni _1-bc Co _b B ¹ _c D ¹ _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2); Li _a Ni _1-bc Co _b B ¹ _c O _2-α F ¹ _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2); Li _a Ni _1-bc Co _b B ¹ _c O _2-α F ¹ ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2); Li _a Ni _1-bc Mn _b B ¹ _c D ¹ _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2); Li _a Ni _1-bc Mn _b B ¹ _c O _2-α F ¹ _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2); Li _a Ni _1-bc Mn _b B ¹ _c O _2-α F ¹ ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α <2); Li _a Ni _b E _c G _d O ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, and 0.001 ≦ d ≦ 0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, and 0.001 ≦ e ≦ 0.1); Li _a NiG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a Mn ₂ G _b O ₄ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiI ¹ O ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≦ f ≦ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≦ f ≦ 2); Compounds represented by any of the formulas of LiFePO ₄ can be used:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or combinations thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

For example, LiCoO ₂ , LiMn _x O _2x (x = 1, 2), LiNi _1-x Mn _x O _2x (0 <x <1), LiNi _1-xy Co _x Mn _y O ₂ (0 ≦ _x ≦ 0.5, 0 ≦ y ≦ 0.5), LiFePO _4, and the like.

What has a coating layer on the surface of the said compound can also be used, or the compound and the compound which have a coating layer can be used in mixture. This coating layer may comprise a coating element compound of an oxide of a coating element, a hydroxide, an oxy hydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. The compounds constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof may be used. The coating layer forming process may use any coating method as long as it can be coated with the above compounds by a method that does not adversely affect the physical properties of the positive electrode active material (for example, spray coating or dipping method). Detailed descriptions thereof will be omitted since they can be understood by those skilled in the art.

Carbon black, graphite fine particles and the like may be used as the conductive material, but is not limited thereto, and any conductive material may be used as long as it can be used as a conductive material in the art.

The binder may include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber-based polymers. It may be used, but not limited to these, any one that can be used as a binder in the art can be used.

N-methylpyrrolidone, acetone or water may be used as the solvent, but is not limited thereto, and any solvent may be used as long as it can be used in the art.

The content of the positive electrode active material, the conductive material, the binder, and the solvent is at a level commonly used in lithium batteries. At least one of the conductive material, the binder, and the solvent may be omitted according to the use and configuration of the lithium battery.

Next, a lithium metal negative electrode is prepared.

The lithium metal cathode is a lithium metal thin film or a lithium metal alloy thin film.

 The lithium metal or lithium metal alloy used as the lithium metal electrode has a thickness of 700 µm or less, for example, 80 µm or less and 0.1 to 60 µm. Specifically, the thickness of the lithium metal or the lithium metal alloy is 1 to 25 μm, for example 5 to 20 μm.

The lithium metal alloy includes lithium metal and metals / metalloids or oxides thereof alloyable with lithium metal. Metals / metalloids or oxides thereof that can be alloyed with lithium metal include Si, Sn, Al, Ge, Pb, Bi, Sb, and Si-Y alloys (Y is an alkali metal, an alkaline earth metal, an element of Group 13, an element of Group 14, Transition metal, rare earth element or combination thereof, not Si), Sn-Y alloy (Y is alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element or combination element thereof , Sn is not), MnOx (0 <x <2) and the like.

As the element Y, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof. For example, the oxide of the metal / metalloid alloyable with the lithium metal may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, SnO ₂ , SiO _x (0 <x <2), or the like.

Next, a separator to be inserted between the positive electrode and the negative electrode is prepared.

The separator may be used as long as it is commonly used in lithium batteries. A low resistance to the ion migration of the electrolyte and excellent in the ability to hydrate the electrolyte can be used. For example, it is selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in a nonwoven or woven form. For example, a rollable separator such as polyethylene or polypropylene may be used for a lithium ion battery, and a separator having excellent organic electrolyte solution impregnation ability may be used for a lithium ion polymer battery. For example, the separator may be manufactured according to the following method.

A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition may be directly coated and dried on the electrode to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film separated from the support may be laminated on the electrode to form a separator.

The polymer resin used to manufacture the separator is not particularly limited, and any materials used for the binder of the electrode plate may be used. For example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate or mixtures thereof and the like can be used.

Next, the above-mentioned organic electrolyte solution is prepared. The organic electrolyte may be easily prepared by those skilled in the art by a method known in the art.

As shown in FIG. 5, the lithium metal secondary battery 1 includes a positive electrode 3, a lithium metal negative electrode 2, and a separator 4. The positive electrode 3, the lithium metal negative electrode 2, and the separator 4 described above are wound or folded to be accommodated in the battery case 5. Subsequently, the organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium battery 1. The battery case 5 may be cylindrical, rectangular, thin film, or the like. For example, the lithium metal secondary battery 1 may be a thin film type battery. The lithium metal secondary battery 1 may be a lithium ion battery.

A separator may be disposed between the positive electrode and the lithium metal negative electrode to form a battery structure. The battery structure is stacked in a bi-cell structure, and then impregnated in an organic electrolyte, and the resultant is accommodated in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery structures may be stacked to form a battery pack, and the battery pack may be used in any device requiring high capacity and high power. For example, it can be used in notebooks, smartphones, electric vehicles and the like.

In addition, the lithium metal secondary battery may be used in an electric vehicle (EV) because of its excellent life characteristics and high rate characteristics. For example, it may be used in a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV). It can also be used in applications where a large amount of power storage is required. For example, it can be used for electric bicycles, power tools and the like.

The present invention is described in more detail through the following examples and comparative examples. However, the examples are provided to illustrate the present invention, and the scope of the present invention is not limited only to these examples.

EXAMPLE

(Production of electrolyte)

Preparation Example 1

Dimethoxyethane (DME) was prepared as an organic solvent, and lithium bis (fluorosulfonyl) imide (LiFSI) was dissolved in the organic solvent to a concentration of 3M to prepare an organic electrolyte solution.

Preparation Example 2

Instead of dimethoxyethane (DME) as the organic solvent, dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) An organic electrolyte solution was prepared in the same manner as in Preparation Example 1, except that a mixed solvent mixed in a volume ratio of: 20 was used.

Preparation Example 3

Instead of dimethoxyethane (DME) as the organic solvent, dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl-1H, 1H, 5H-octafluoropentylether (HFE6512) were 80:20 An organic electrolyte solution was prepared in the same manner as in Preparation Example 1, except that a mixed solvent mixed in a volume ratio of was used.

Preparation Example 4

Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as organic solvents are mixed in a volume ratio of 2: 5: 3 (EC: EMC: DEC). One carbonate solvent was prepared.

Next, lithium hexafluorophosphate (Lithium hexafluorophosphate, LiPF ₆ ) as a lithium salt was dissolved in the carbonate solvent so that the molar concentration of the lithium salt was 1.15 M to prepare an organic electrolyte solution.

Preparation Example 5

1 wt% of fluoroethylene carbonate (FEC) was added to the organic electrolyte solution obtained in Preparation Example 1 to prepare an organic electrolyte solution.

Preparation Example 6

Lithium difluoro (oxalate) borate (LiDFOB) was added to the organic electrolyte solution obtained in Preparation Example 1 to prepare an organic electrolyte solution.

Preparation Example 7

1 wt% of fluoroethylene carbonate (FEC) was added to the organic electrolyte solution obtained in Preparation Example 4 to prepare an organic electrolyte solution.

Preparation Example 8

1 wt% of fluoroethylene carbonate (FEC) was added to the organic electrolyte solution obtained in Preparation Example 2, thereby preparing an organic electrolyte solution.

Preparation Example 9

1 wt% of lithium difluoro (oxalate) borate (LiDFOB) was added to the organic electrolyte solution obtained in Preparation Example 2, thereby preparing an organic electrolyte solution.

Preparation Example 10

Lithium difluorobis (oxalato) phosphate (WCA2) was added to the organic electrolyte solution obtained in Preparation Example 1 to prepare an organic electrolyte solution.

Preparation Example 11

1 wt% of fluoroethylene carbonate (FEC) was added to the organic electrolyte solution obtained in Preparation Example 3 to prepare an organic electrolyte solution.

Preparation Example 12

1 wt% of lithium difluoro (oxalate) borate (LiDFOB) was added to the organic electrolyte solution obtained in Preparation Example 3 to prepare an organic electrolyte solution.

Preparation Example 13

Lithium difluorobis (oxalato) phosphate (WCA2) was added to the organic electrolyte solution obtained in Preparation Example 1 to prepare an organic electrolyte solution.

Evaluation Example 1 Evaluation of Oxidation Stability of Electrolyte

Example 1

A 2016 type coin cell was fabricated by a conventionally known method using a lithium metal foil as a counter electrode, stainless steel as a working electrode, and an organic electrolyte solution obtained in Preparation Example 11 as an electrolyte.

Comparative Examples 1 to 5

Instead of the organic electrolyte obtained in Preparation Example 11, except that the organic electrolyte obtained in Preparation Examples 1, 3, 4, 5, and 7, respectively, was prepared in the same manner as in Example 1, 2016 type coin cell.

Evaluation method and result

The coin cells prepared in Example 1 and Comparative Examples 1, 3, 4, 5, and 7 were analyzed for electrolyte oxidation stability by linear sweep voltammetry (LSV). The linear scanning potential method proceeds by measuring the current value with respect to the voltage of the coin cell over time while scanning the potential of the working electrode at a constant speed of 1.0 mV / s.

As a result, as shown in Fig. 1 (a), the 3M LiFSI DME composition without the fluorinated solvent (HFE6512) generates low current from about 4.2 V (vs. Li / Li ⁺ ) and the amount of oxidation current from 5.0 V Increase sharply. After mixing DME and HFE6512 in a volume ratio of 80:20, 3M LiFSI DME / HFE6512 (8/2) composition prepared by adding 3M LiFSI begins to generate low current from about 4.4 V, and the amount of oxidation current from 5.0 V Increase sharply. According to FIG. 1 (b), it can be seen that the amount of low current generated at about 4.5 V was decreased in the electrolyte solution in which 1 wt% FEC was added to the 3M LiFSI DME and 3M LiFSI DME / HFE6512 (8/2).

Evaluation Example 2: Evaluation of Lifetime Characteristics According to Lithium Electrodeposition / Desorption Reaction

Example 2

A 2016 type coin cell was manufactured by a conventionally known method using a lithium metal foil as a counter electrode, a copper (Cu) foil as a working electrode, and an organic electrolyte solution obtained in Preparation Example 11 as an electrolyte.

Comparative Examples 6 to 12

Instead of the organic electrolyte solution obtained in Preparation Example 11, except that the organic electrolyte solution obtained in Preparation Examples 1 to 5, 7 and 8 was used in the same manner as in Example 2 to produce a 2016 type coin cell.

Cycle characteristic evaluation

The current of 7.33 mAh (4.15 mAh / cm ² ) was cut-off after charging for 10 hours at a constant current of 0.1 C, and then discharged to 1 V under a constant current of 0.1 C, and then cut-off. Turned off. After the initial charge and discharge, the cycle life characteristics were evaluated by performing charge and discharge 200 times at 0.5 ° C. at 25 ° C., and the coulombic efficiency for each cycle was calculated and shown in FIG. 2.

According to FIG. 2 (a), the existing carbonate electrolyte 1.15 M LiPF ₆ EC / EMC / DEC (2/5/3) has a coulombic efficiency lower than 50% during the initial six cycles. When 1 wt% of FEC, a cathode interfacial stabilizer, is added, the coulombic efficiency is improved to about 70%, but the coulombic efficiency is drastically reduced after 10 cycles. The 3 M LiFSI DME lasts up to 100 cycles, but the 100-cycle lithium electrodeposits produce a high overvoltage and stop the cell. In addition, the electrolyte containing FEC as an additive has a lifespan reduced by about 25 times when evaluated at a high rate of 0.5 C. It can be seen that the SEI layer formed of FEC acted as a resistive layer at a high rate of 0.5C. According to FIG. 2 (b), the 3 M LiFSI DME / TTE (8/2) has a lifespan of up to about 125 times. This is because the SEI layer formed by TTE in chemical charge / discharge continuously suppresses the decomposition reaction between lithium and the electrolyte solution during the cycle and did not act as a resistance. However, when FEC is added, the coulombic efficiency decreases after 70 cycles. Meanwhile, the 3M LiFSI DME / HFE6512 (2/8) composition containing 20% by volume of HFE6512 was cycled at a high coulombic efficiency of 99.3% up to 200 times. In addition, the HFE6512 does not cause a decrease in life characteristics at high rates even with the addition of FEC, and the cycle proceeded with a stable C-rate of 98.7% up to 200 times. Thus, it can be seen that FEC does not act as a resistance when using a HFE6512 fluorinated solvent.

Evaluation Example 3: Evaluation of Battery Characteristics in Full Cell (1)

Example 3

A slurry was prepared by mixing LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode active material: conductive material: binder in a weight ratio of 95: 2.5: 2.5. Here, Super-P was used as the conductive material, and polyvinylidene fluoride (PVdF) was dissolved in N-methyl-2-pyrrolidone solvent as the binder.

The slurry was uniformly applied to the Al current collector, and dried at 110 ° C. for 2 hours to prepare a positive electrode. The loading level of the electrode plate was 10.2 mg cm ⁻² and the electrode density was 2.5 g cm ⁻³ .

The prepared anode was used as a working electrode, lithium metal foil was used as a counter electrode, and a CR2032 coin cell was manufactured according to a commonly known process using an organic electrolyte solution obtained in Preparation Example 9.

Examples 4-5

A CR2032 coin cell was produced in the same manner as in Example 3, except that the organic electrolytes obtained in Preparation Examples 11 and 12 were used instead of the organic electrolyte obtained in Preparation Example 9.

Comparative Examples 13 to 18

A CR2032 coin cell was produced in the same manner as in Example 3, except that the organic electrolytes obtained in Preparation Examples 1 to 6 were used instead of the organic electrolyte obtained in Preparation Example 9.

Charge / discharge characteristic evaluation

For the initial Mars evaluation, the half-cells prepared in Examples 3 to 5 and Comparative Examples 13 to 18 were charged in constant current (CC) mode to 0.1 V at 4.2 C at 0.1 C after 10 hours of rest, followed by a current of 0.02 C. Charged in constant voltage (CV) mode. Subsequently, discharge was performed in CC mode to 3.0V at 0.1C.

After the initial charge and discharge, the discharge capacity and the coulombic efficiency were calculated while performing charge and discharge 70 times at 0.5 ° C. at 25 ° C., and are shown in FIG. 3.

According to FIGS. 3 (a) and 3 (b), the composition of 1.15 M LiPF ₆ EC / EMC / DEC (2/5/3) of the existing carbonate electrolyte showed a decrease in discharge capacity from about 30 cycles, but the 3M LiFSI DME In the composition, the coulombic efficiency remained above about 90% at 70 cycles, regardless of the additive.

According to Figures 3 (c) and (d), the electrolyte of 3M LiFSI DME / TTE (8: 2) LiDFOB composition had a coulombic efficiency of about 100% in about 70 cycles but did not include LiDFOB as an additive. It can be seen that in the electrolyte, the coulombic efficiency drops sharply from about 10 cycles and stops at about 50 cycles. While not being bound by theory, the LiDFOB additive forms a stable SEI film at the anode interface, which can inhibit the oxidative decomposition of the mixed solvent of DME / TTE and LiFSI salt at the anode interface, thus maintaining the coulombic efficiency at about 100% in 70 cycles. Can be.

3 (e) and (f), it can be seen that the discharge capacity and the coulomb efficiency of the battery employing the electrolyte of the 3M LiFSI DME / HFE6512 (8/2) composition decrease as the charge / discharge cycle progresses. On the other hand, when FEC or LiDFOB is added to the 3M LiFSI DME / HFE6512 (8/2) as an additive, a stable SEI layer is formed at the anode interface so that the additive does not oxidize and dissolve in the electrolyte, and the SEI layer has a high voltage. Since the electrolyte prevents side reactions in which the electrolyte receives oxidative decomposition from electrons at the anode interface, the discharge capacity and the coulombic efficiency can be improved. In particular, in the case of the electrolyte solution containing LiDFOB as an additive, side reactions at the anode interface could be more effectively suppressed.

Furthermore, according to Figures 3 (b) and (f), the FEC or LiDFOB additives are equivalent or better when used with the DME / HFE6512 (8: 2) mixed solvent, as compared to the use of DME alone as a solvent. It can be seen that the Coulombic efficiency.

Evaluation Example 4 Evaluation of Battery Characteristics in Full Cell (2)

Example 6

A CR2032 coin cell was manufactured in the same manner as in Example 3, except that the organic electrolyte solution obtained in Preparation Example 10 was used instead of the organic electrolyte solution obtained in Preparation Example 9.

Comparative Examples 19 to 24

The CR2032 coin cell was prepared in the same manner as in Example 3, except that the organic electrolytes obtained in Preparation Examples 1, 2, 4, 8, 9, and 13 were used instead of the organic electrolytes obtained in Preparation Example 9. Produced.

Charge / discharge characteristic evaluation

The coin cells obtained in Example 6 and Comparative Examples 19 to 24 were calculated in the same manner as in the evaluation of the charge and discharge characteristics in Evaluation Example 3, and the discharge capacity and the coulomb efficiency were calculated and shown in FIG. 4.

According to FIG. 4 (a), when 1 wt% FEC and 1 wt% lithium difluorobis (oxalato) phosphate are added to 3M LiFSI DME / TTE, about 160 mAh / g Although the specific capacity of was maintained up to 70 cycles, it can be seen that when the additive of 1 wt% FEC or 1 wt% lithium difluorobis (oxalato) phosphate was not included, the specific cost rapidly decreased. In addition, when 1wt% FEC was added to the 3M LiFSI DME / TTE, only 1wt% FEC and 1wt% lithium difluorobis (oxalato) phosphate were used. It can be seen that the superior cost is maintained up to 70 cycles. That is, it can be seen that the addition of 1wt% lithium difluorobis (oxalato) phosphate (Lithium difluorobis (oxalato) phosphate) improves the specific amount.

In addition, according to FIG. 4B, a coin cell using an electrolyte solution in which 1 wt% FEC and 1 wt% lithium difluorobis (oxalato) phosphate was added to 3M LiFSI DME / TTE was used. In comparison with a coin cell using an electrolyte in which no additives of 1 wt% FEC or 1 wt% lithium difluorobis (oxalato) phosphate are added, it is confirmed that the Coulomb efficiency is excellent.

In the above described a preferred embodiment according to the present invention with reference to the drawings and embodiments, but this is only exemplary, those skilled in the art that various modifications and equivalent other embodiments are possible from this. You will understand. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (14)

Lithium salts; Organic solvents; And an electrolyte solution for a lithium metal secondary battery comprising an additive,
The concentration of the lithium salt is 3M to 4M,
The organic solvent includes an ether solvent and a fluorinated solvent,
The volume ratio of the ether solvent and the fluorinated solvent is 90:10 to 60:40,
The ether solvent is selected from a glyme solvent,
The glymeic solvent is included in 70% by volume to 90% by volume, based on the total volume of the electrolyte,
The fluorinated solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3, tetrafluoropropylether, and the additive is lithium difluoro (oxalato) borate, or fluoro A combination of ethylene carbonate and lithium difluorobis (oxalato) phosphate, or
The fluorinated solvent is 1,1,2,2-tetrafluoroethyl-1H, 1H, 5H-octafluoropentyl ether, the additive is fluoroethylene carbonate, lithium difluoro (oxalato) borate, An electrolyte solution for lithium metal secondary batteries, selected from lithium difluorobis (oxalato) phosphate, and combinations thereof. The method of claim 1,
The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiBOB, LiTFSI, LiFSI, LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , For a lithium metal secondary battery selected from LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (x, y is 1 to 20), LiCl, LiI or mixtures thereof Electrolyte solution. delete The method of claim 1,
The electrolyte solution for lithium metal secondary batteries, wherein the glyme solvent is 1,2-dimethoxyethane, 1,3-dioxolane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or a combination thereof. delete delete The method of claim 1,
The fluorinated solvent is 1,1,2,2-tetrafluoroethyl-1H, 1H, 5H-octafluoropentyl ether, and the additive is fluoroethylene carbonate or lithium difluoro (oxalato) borate Electrolyte for phosphorus and lithium metal secondary batteries. The method of claim 1,
The fluorinated solvent is included in 10% by volume to 30% by volume, based on the total volume of the electrolyte, lithium metal secondary battery electrolyte. delete delete delete delete The method of claim 1,
The additive is included 1 part by weight or more based on 100 parts by weight of the electrolyte, the electrolyte solution for lithium metal secondary batteries. anode; A negative electrode comprising lithium metal; And a lithium metal secondary battery electrolyte according to any one of claims 1, 2, 4, 7, 8, and 13.

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