KR102468498B1 - Electrolyte and Lithium Metal Electrode Comprising the Same - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium metal battery, and more particularly, an ionic liquid containing a cationic group and an anionic group is used as an electrolyte for a lithium metal battery, and the growth of lithium dendrites by controlling the length of an aliphatic chain bound to the cationic group can be suppressed, and the performance of a lithium metal battery can be improved even with a small amount of additives.

Description

Electrolyte and lithium metal battery containing the same {Electrolyte and Lithium Metal Electrode Comprising the Same}

The present invention relates to an electrolyte capable of improving battery performance by suppressing growth of lithium dendrites in a lithium metal battery including lithium metal as an anode and a lithium metal battery including the same.

As electric, electronic, communication, and computer industries rapidly develop, demand for high-performance and high-stability secondary batteries has recently increased rapidly. In particular, according to the trend of light weight, thinness, miniaturization, and portability of batteries and electronic products, light weight and miniaturization of secondary batteries, which are core components, is required. In addition, as the need for a new type of energy supply source has emerged due to environmental pollution and pomegranate exhaustion, the need for developing an electric vehicle capable of solving these problems has increased. Among various secondary batteries, lithium secondary batteries that are lightweight, exhibit high energy density and operating potential, and have a long cycle life have recently been in the limelight.

A lithium secondary battery has a structure in which electrode assemblies including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are stacked or wound, and the electrode assembly is embedded in a battery case and a non-aqueous electrolyte is injected into the battery case. . At this time, the capacity of the lithium secondary battery is different depending on the type of electrode active material, and since a sufficient capacity is not secured as much as the theoretical capacity during actual driving, it has not been commercialized.

Metal-based materials such as silicon (4,200 mAh/g) and tin (990 mAh/g), which exhibit high storage capacity characteristics through an alloying reaction with lithium, are used as negative electrode active materials for high capacity lithium secondary batteries. However, when a metal such as silicon or tin is used as an anode active material, the volume expands approximately four times during the charging process of alloying with lithium and contracts during discharging. Due to the large volume change of the electrode that occurs repeatedly during charging and discharging, the active material is gradually pulverized and detached from the electrode, resulting in a rapid decrease in capacity.

Compared to the anode active materials mentioned above, lithium metal has an excellent theoretical capacity of 3,860 mAh/g and a very low standard hydrogen electrode (SHE) of -3.045 V, enabling the realization of high-capacity and high-energy density batteries. , A lot of research is being conducted on a lithium metal battery (LMB) using lithium metal as an anode active material of a lithium secondary battery.

However, due to the high chemical/electrochemical reactivity of lithium metal, lithium metal batteries react easily with electrolytes, impurities, and lithium salts to form a solid electrolyte interphase (SEI) on the surface of the electrode, and such a passivation layer forms a solid electrolyte interphase (SEI) on the surface of the electrode. Dendritic dendrites form on the lithium metal surface, resulting in a density difference. The lithium dendrite not only shortens the lifespan of the lithium secondary battery, but also causes an internal short circuit and dead lithium to increase the physical and chemical instability of the lithium secondary battery, reduce the capacity of the battery, shorten the cycle life, and adversely affect the stability of In addition, the passivation layer is thermally unstable, so that charging and discharging of the battery continuously proceeds, or, in particular, when stored at high temperature in a fully charged state, it may be slowly disintegrated by increased electrochemical energy and thermal energy. Due to the collapse of the passivation layer, a side reaction in which the exposed lithium metal surface directly reacts with the electrolyte solvent and decomposes continuously occurs, thereby increasing the resistance of the negative electrode and lowering the charge / discharge efficiency of the battery. In addition, when the passivation layer is formed, the solvent of the electrolyte is consumed, and the life of the battery is reduced due to by-products and gases generated during various side reactions such as formation and collapse of the passivation layer and decomposition of the electrolyte.

Due to such high instability of lithium metal, a lithium metal battery using lithium metal as an anode has not been commercialized.

In order to solve this problem, various methods such as introducing a protective layer on the surface of lithium metal or changing the composition of an electrolyte have been studied.

For example, Korean Patent Publication No. 2017-0028391 relates to an all-solid-state battery including a layer of a solid electrolyte and a polymer material, and discloses a solid electrolyte including a polymer material of an ionic group in an electrolyte material layer. The polymer material of the ionic group is n-propyl-n-methylpyrrolidinium (PYR13), n-butyl-n-methylpyrrolidinium, etc. as a cation; Disclosed is a polymeric material composed of bis(fluorosulfonyl)imide or the like as an anion. Still unsatisfactory results are shown in terms of the effect of inhibiting lithium dendrite growth and improving the performance of the battery.

In addition, in a lithium metal battery using lithium metal as an anode, there is a further need to develop a technology capable of stabilizing the interface of lithium metal, which is an anode.

Korean Patent Publication No. 2017-0028391, "All-Solid Battery Containing Layers of Solid Electrolyte and Polymer Material"

As a result of various studies to solve the above problems, the present inventors have found that as an electrolyte additive included in a lithium metal battery, a pyrrolidinium functional group attached with a long non-polar aliphatic chain and a bis(fluorosulfonyl) As a result of using a small amount of an ionic liquid containing a phonyl)imide functional group, the long non-polar aliphatic chain-attached pyrrolidinium disperses charge aggregation on the surface of lithium metal to suppress lithium dendrite growth, and the bis( It was confirmed that fluorosulfonyl)imide can maintain high efficiency by forming a LiF-rich film on the surface of lithium metal.

Accordingly, an object of the present invention is to provide an electrolyte for a lithium metal battery capable of suppressing the growth of lithium dendrites and improving battery performance.

Another object of the present invention is to provide a lithium metal battery including the electrolyte for a lithium metal battery.

In order to achieve the above object, the present invention is an electrolyte for a lithium metal battery comprising an organic solvent, a lithium salt and an additive, wherein the additive is an ionic liquid, the ionic liquid is a cation, a C ₆ to C ₁₂ alkyl group substituted with pyrrolidinium, and the ionic liquid contains bis(fluorosulfonyl)imide as an anion, providing an electrolyte for a lithium metal battery.

The additive may be represented by Formula 1 below.

[Formula 1]

1-X-1-methylpyrrolidinium bis(fluorosulfonyl)imide

In the above formula, X may be a C ₆ to C ₁₂ alkyl group, or the X may be a C ₉ to C ₁₂ alkyl group.

The additive may be included in an amount of 10 to 30% by weight based on the total weight of the electrolyte.

The additive may be included in an amount of 15 to 25% by weight based on the total weight of the electrolyte.

The organic solvent may be at least one selected from the group consisting of ether-based solvents, ester-based solvents, amide-based solvents, linear carbonate-based solvents, and cyclic carbonate-based solvents.

The lithium salt is LiFSI, LiPF ₆ , LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, and lithium 4-phenyl borate.

The present invention also provides a lithium metal battery including the electrolyte.

The electrolyte for a lithium metal battery according to the present invention can enhance the stability of a lithium metal battery while maintaining the physical properties required for a lithium metal battery, such as ion conductivity and wettability, at the same level as those of conventional lithium metal batteries.

In addition, the electrolyte for a lithium metal battery uses an ionic liquid as an additive, but uses a functional group, for example, pyrrolidinium, which exhibits strong characteristics against reduction as a cation contained in the ionic liquid, so that the surface of the lithium metal It is possible to inhibit lithium dendrite growth by dispersing charge aggregation in

In addition, by controlling the length of the aliphatic chain bonded to the pyrrolidinium, the lithium dendrite growth inhibitory effect can be further enhanced.

In addition, high efficiency of the battery can be maintained by using a functional group, for example, bisfluorosulfonylimide, which can form a LiF-rich film on the surface of lithium metal by being decomposed as an anion contained in the ionic liquid. have.

1 is a result of measuring coulombic efficiency according to charge and discharge cycles for Li-Cu asymmetric cells manufactured in Examples and Comparative Examples.
2a and 2b are results obtained by measuring coulombic efficiencies according to charge/discharge cycles for Li-Cu asymmetric cells prepared in Example 1 and Comparative Example 5 under different charging and discharging conditions.
Figure 3a is a graph showing the results of the charge and discharge test for the Li-LFP full cell prepared in Example 1, Comparative Example 1, and Comparative Example 5, respectively. 3B is a SEM photograph showing a cross-section of a lithium metal negative electrode after 120 cycles of charging and discharging for Li-LFP full cells prepared in Example 1, Comparative Example 1, and Comparative Example 5, respectively.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

Terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Electrolyte for lithium metal battery

The present invention relates to an electrolyte for a lithium metal battery, and by controlling the composition of the electrolyte, it is possible to enhance stability by suppressing the growth of lithium dendrites while maintaining performance equal to or higher than that of a conventional lithium metal battery.

In the present invention, "lithium metal battery" means a secondary battery using lithium metal as a negative electrode.

Unlike salt, where ionic salt compounds composed of metal cations and non-metal anions usually melt at high temperatures of 800° C. or higher, ionic liquids are ionic salts that exist as liquids at temperatures of 100° C. or lower. In particular, an ionic liquid that exists as a liquid at room temperature is referred to as a room temperature ionic liquid (RTIL).

Since ionic liquids are non-volatile, they have no vapor pressure and have high ionic conductivity. In particular, since it has a unique property of dissolving inorganic and organometallic compounds well and existing as a liquid in a wide temperature range due to its high polarity, it can be applied to a wide range of chemical fields such as catalysis, separation, and electrochemistry. And low symmetry, weak intermolecular forces and charge distribution in cations reduce the melting point.

In addition, ionic liquids are non-toxic, non-flammable, and have excellent thermal stability, as well as a wide temperature range as a liquid, high solvation ability, and non-coordinated bonds, etc., which are environmentally friendly next-generation solvents that can replace conventional toxic organic solvents. It has physicochemical properties as

The unique physical and chemical properties of ionic liquids are greatly influenced by the structure of cations and anions in ionic liquids, and can be optimized according to the user's purpose of use.

The ionic liquid according to the present invention includes pyrrolidinium as a cation, but the pyrrolidinium may be substituted with a non-polar aliphatic chain, specifically, a C ₆ to C ₁₂ alkyl group.

Since the pyrrolidinium exhibits a strong reduction property, it can serve to inhibit the growth of lithium dendrites by dispersing charge aggregation on the surface of the lithium metal. At this time, the characteristic that is resistant to reduction means a characteristic that the reduction potential is relatively low compared to other solvents. When lithium metal is used as a negative electrode, since the reduction potential is 0V, it is preferable to apply an organic solvent and electrolyte that are not reduced and stable even at 0V.

In addition, depending on the length of the C ₆ to C ₁₂ alkyl group bonded to the pyrrolidinium as a substituent, the lithium dendrite growth inhibitory effect may vary. For example, the length of the C ₆ to C ₁₂ alkyl group The longer the length, the better the lithium dendrite growth inhibitory effect.

The ionic liquid according to the present invention may include bis(fluorosulfonyl)imide as an anion, and the bisfluorosulfonylimide is decomposed to form a LiF-rich film on the surface of lithium metal This can play a role in maintaining high efficiency.

In the present invention, the additive may be represented by Formula 1 below.

[Formula 1]

1-X-1-methylpyrrolidinium bis(fluorosulfonyl)imide

In the above formula, X is a C ₆ to C ₁₂ alkyl group.

In addition, X in the above formula may be a C ₉ to C ₁₂ alkyl group, and in this case, the repulsive force with lithium ions on the surface of the lithium metal increases, so that the effect of inhibiting the growth of lithium dendrites can be further improved.

In the present invention, the additive may be included in an amount of 10 to 30 wt%, preferably 15 to 30 wt%, and more preferably 20 to 30 wt% based on the total weight of the electrolyte. If the content of the additive is less than the above range, the effect of inhibiting the growth of lithium dendrite may be insignificant, and if the content exceeds the above range, battery performance may be rather deteriorated.

In the present invention, the electrolyte for a lithium metal battery may include an organic solvent. As the organic solvent, ether, ester, amide, linear carbonate, cyclic carbonate, etc. may be used alone or in combination of two or more.

The ether compounds include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene Glycol Diethyl Ether, Diethylene Glycol Methylethyl Ether, Triethylene Glycol Dimethyl Ether, Triethylene Glycol Diethyl Ether, Triethylene Glycol Methylethyl Ether, Tetraethylene Glycol Dimethyl Ether, Tetraethylene Glycol Diethyl Ether, Tetraethylene Glycol Methylethyl At least one selected from the group consisting of ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methylethyl ether, 1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran may be used, It is not limited to this.

Examples of the ester include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σσ-valerolactone And ε-caprolactone, but any one selected from the group consisting of, or a mixture of two or more of them may be used, but is not limited thereto.

Specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate, or any one of these Mixtures of two or more kinds may be used representatively, but are not limited thereto.

In addition, specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate , 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and any one selected from the group consisting of halides thereof, or a mixture of two or more thereof. These halides include, for example, fluoroethylene carbonate (FEC) and the like, but are not limited thereto.

In addition, there are N-methylpyrrolidone, dimethyl sulfoxide, sulfolane and the like in addition to the organic solvents described above.

The electrolyte for a lithium metal battery of the present invention may further include a nitric acid-based compound commonly used in the art in addition to the above-described composition. For example, lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), cesium nitrate (CsNO ₃ ), magnesium nitrate (MgNO ₃ ), barium nitrate (BaNO ₃ ), lithium nitrite (LiNO ₂ ), potassium nitrite (KNO ₂ ) ), cesium nitrite (CsNO ₂ ), and the like.

In the present invention, the electrolyte for a lithium metal battery may include a lithium salt as an electrolyte salt. The lithium salt is not particularly limited in the present invention, and may be used without limitation as long as it is commonly used in an electrolyte for a lithium secondary battery.

For example, the lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₄ BO ₈ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi . Preferably, the lithium salt may be lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or (CF ₃ SO ₂ ) ₂ NLi.

The concentration of the lithium salt may be appropriately determined in consideration of ionic conductivity, solubility, and the like, and may be, for example, 0.1 to 4.0 M, preferably 0.5 to 2.0 M. If the concentration of the lithium salt is less than the above range, it is difficult to secure ion conductivity suitable for battery driving. Since the performance of the battery may deteriorate, it is appropriately adjusted within the above range.

lithium metal battery

The present invention provides a lithium metal battery including the electrolyte for the lithium metal battery.

The lithium metal battery includes a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode, and includes the electrolyte for a lithium metal battery according to the present invention as the electrolyte.

The positive electrode may include a positive electrode current collector and a positive electrode active material coated on one or both surfaces of the positive electrode current collector.

The cathode current collector supports the cathode active material and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. may be used.

The cathode current collector may form fine irregularities on its surface to enhance bonding strength with the cathode active material, and various forms such as films, sheets, foils, meshes, nets, porous materials, foams, and nonwoven fabrics may be used.

The cathode active material may include a cathode active material and optionally a conductive material and a binder.

The cathode active material is elemental sulfur (Elemental sulfur, S ₈ ); Li ₂ S _n (n≥≥1), 2,5-dimercapto-1,3,4-thiadiazole, 1,3,5-tri Sulfur such as disulfide compounds such as 1,3,5-trithiocyanuic acid, organosulfur compounds, or carbon-sulfur polymers ((C ₂ S _x ) _n : x=2.5 to 50, n≥≥2) It may be one or more selected from the group consisting of containing compounds. Preferably, inorganic sulfur (S ₈ ) may be used.

The positive electrode may further include one or more additives selected from a transition metal element, a group IIIA element, a group IVA element, a sulfur compound of these elements, and an alloy of these elements and sulfur, in addition to the positive electrode active material.

The transition metal elements include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au or Hg and the like are included, the IIIA group elements include Al, Ga, In, Ti, and the like, and the IVA group elements may include Ge, Sn, Pb, and the like.

The conductive material is for improving electrical conductivity, and is not particularly limited as long as it is an electronically conductive material that does not cause chemical change in a lithium secondary battery.

In general, carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material, etc. can be used. Acetylene black series (chevron chemical Company (such as from Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (from Armak Company), Vulcan XC-72 (from Cabot Company) (manufactured by Cabot Company) and Super P (manufactured by MMM). For example, acetylene black, carbon black, graphite, etc. are mentioned.

In addition, the cathode active material may further include a binder having a function of maintaining the cathode active material in the cathode current collector and connecting the active materials. As the binder, for example, polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, poly methyl methacrylate, styrene butadiene rubber (SBR), carboxyl methyl cellulose (CMC), poly(acrylic acid) (PAA), polyvinyl alcohol (poly Various types of binders such as (vinyl alcohol) and PVA) may be used.

The negative electrode may include a negative electrode current collector and an negative electrode active material disposed on the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate.

The anode current collector is for supporting the anode active material, and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of a lithium secondary battery. For example, copper, stainless steel, aluminum, nickel, titanium, Palladium, fired carbon, copper or stainless steel surface treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. may be used.

The negative electrode current collector may form fine irregularities on its surface to enhance bonding strength with the negative electrode active material, and various forms such as films, sheets, foils, meshes, nets, porous bodies, foams, and nonwoven fabrics may be used.

The anode active material includes a material capable of reversibly intercalating or deintercalating lithium (Li ⁺ ), a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal, or a lithium alloy. can do. The material capable of reversibly intercalating or releasing lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. A material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion (Li ⁺ ) may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy is, for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( It may be an alloy of a metal selected from the group consisting of Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn). Preferably, the negative electrode active material may be lithium metal, and specifically, may be in the form of a lithium metal thin film or lithium metal powder.

The method of forming the negative electrode active material is not particularly limited, and a method of forming a layer or film commonly used in the art may be used. For example, methods such as compression, coating, and deposition may be used. In addition, a case in which a metal lithium thin film is formed on a metal plate by initial charging after assembling a battery in a state in which the lithium thin film is not present on the current collector is also included in the negative electrode of the present invention.

The electrolyte includes lithium ions, and is used to cause an electrochemical oxidation or reduction reaction at the positive electrode and the negative electrode through the lithium ion, as described above.

Injection of the electrolyte solution may be performed at an appropriate stage during the manufacturing process of the electrochemical device according to the manufacturing process and required physical properties of the final product. That is, it may be applied before assembling the electrochemical device or at the final stage of assembling the electrochemical device.

A separator may be additionally included between the anode and cathode described above. The separator is for physically separating both electrodes in the lithium secondary battery of the present invention, and can be used without particular limitation as long as it is normally used as a separator in a lithium secondary battery. It is desirable to have excellent ability.

The separator may be made of a porous substrate. As for the porous substrate, any porous substrate commonly used in an electrochemical device may be used. For example, a polyolefin-based porous membrane or non-woven fabric may be used, but is not particularly limited thereto. .

Examples of the polyolefin-based porous membrane include polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, and polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, each alone or a mixture thereof. one membrane.

In addition to the polyolefin-based nonwoven fabric, the nonwoven fabric includes, for example, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, and polycarbonate. ), polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalate, respectively, alone or a non-woven fabric formed of a polymer obtained by mixing them. The structure of the nonwoven fabric may be a spunbond nonwoven fabric or a melt blown nonwoven fabric composed of long fibers.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm.

The size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.001 to 50 μm and 10 to 95%, respectively.

The lithium secondary battery according to the present invention may perform lamination and stacking and folding processes of separators and electrodes in addition to winding, which is a general process.

The shape of the lithium secondary battery is not particularly limited and may be of various shapes such as a cylindrical shape, a laminated shape, and a coin shape.

In addition, the present invention provides a battery module including the lithium metal battery as a unit cell.

The battery module may be used as a power source for medium or large-sized devices requiring high temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the medium-large device include a power tool powered by an omniscient motor and moving; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; A power storage system, etc. may be mentioned, but is not limited thereto.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the following examples are merely illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It goes without saying that changes and modifications fall within the scope of the appended claims.

The compositions of the electrolytes prepared in Example 1 and Comparative Examples 1 to 5 are shown in Table 1, and each electrolyte, Li│Cu asymmetric cell and Li│LFP full cell were prepared by varying additives and additive contents.

electrolyte organic solvent lithium salt additive additive content Example 1 DOL/DME (1/1) 1 M LiTFSI Pyr1(12) FSI ^{note 1 )} 30% by weight Comparative Example 1 DOL/DME (1/1) 1 M LiTFSI - 0% by weight Comparative Example 2 DOL/DME (1/1) 1 M LiTFSI Im1(4) TFSI ^{note 2 )} 29% by weight Comparative Example 3 DOL/DME (1/1) 1 M LiTFSI Im1(4) FSI ^{note 3 )} 24% by weight Comparative Example 4 DOL/DME (1/1) 1 M LiTFSI Pyr1(4) TFSI ^{Note 4 )} 29% by weight Comparative Example 5 DOL/DME (1/1) 1 M LiTFSI Pyr1(4) FSI ^{Note 5 )} 24% by weight Note 1) Pyr1(12) FSI: 1-Dodecyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide
Note 2) Im1(4) TFSI: 1-Butyl-1-methylimidazolium bis(trifluoromethylsulfonyl)imide
Note 3) Im1(4) FSI: 1-Butyl-1-methylimidazolium bis(fluorosulfonyl)imide
Note 4) Pyr1(4) TFSI: 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide
Note 5) Pyr1(4) FSI: 1-Butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide

Example One

(1) Manufacture of electrolyte

A solution of 1.0 M LiTFSI dissolved in an organic solvent consisting of 1,3-dioxolane and dimethyl ether (DOL:DME=1:1 (volume ratio)) was prepared, and 1-dodecyl-1-methylpyrroly was added to the solution. An electrolyte was prepared by adding 30% by weight of dinium bis(fluorosulfonyl)imide (Pyr1(12) FSI, 1-Dodecyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide).

(2) Manufacturing of Li│Cu asymmetric cell

A Li│Cu asymmetric cell was prepared using a lithium metal thin film having a thickness of 40 μm as an anode and 70 μl of the electrolyte.

(3) Li│LFP complete cell manufacturing

A LiFePO ₄ electrode having a thickness of 40 μm was used as an anode (LFP), and a lithium metal thin film having a thickness of 40 μm was used as a cathode (Li).

After placing the prepared anode and cathode to face each other and placing a polyethylene separator therebetween, 70 μl of the electrolyte was injected to prepare a Li│LFP full cell.

comparative example One

An asymmetric cell and a full cell were prepared in the same manner as in Example 1, but using an electrolyte prepared without using an additive.

comparative example 2

It was carried out in the same manner as in Example 1, but as an additive, 1-butyl-1-methylimidazolium bis (trifluoromethylsulfonyl) imide (1-Butyl-1-methylimidazolium bis (trifluoromethylsulfonyl) imide, Im1 (4 ) TFSI) asymmetric cells and full cells were prepared using the prepared electrolyte using 29% by weight.

comparative example 3

It was carried out in the same manner as in Example 1, but as an additive, 1-butyl-1-methylimidazolium bis (fluorosulfonyl) imide (1-Butyl-1-methylimidazolium bis (fluorosulfonyl) imide, Im1 (4) FSI ), asymmetric cells and full cells were prepared using the prepared electrolyte using 24% by weight.

comparative example 4

It was carried out in the same manner as in Example 1, but as an additive, 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide (1-Butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide, Pyr1 (4 ) TFSI) asymmetric cells and full cells were prepared using the prepared electrolyte using 29% by weight.

comparative example 5

It was carried out in the same manner as in Example 1, but as an additive, 1-butyl-1-methylpyrrolidinium bis (fluorosulfonyl) imide (1-Butyl-1-methylpyrrolidinium bis (fluorosulfonyl) imide, Pyr1 (4) FSI ), asymmetric cells and full cells were prepared using the prepared electrolyte using 24% by weight.

Experimental example 1: Battery performance evaluation according to the type of additives included in the electrolyte

For the asymmetric cell including the electrolyte prepared with different types of additives, the cell performance was evaluated by measuring the coulombic efficiency according to the progress of charge and discharge cycles. Experimental conditions were 1 mA·cm ⁻² charge/1 mA·cm ⁻² discharge conditions, and after charging and discharging were performed for 50 cycles, coulombic efficiency was evaluated.

1 is a result of measuring coulombic efficiency according to charge and discharge cycles for Li-Cu asymmetric cells manufactured in Examples and Comparative Examples. Table 2 below shows the Coulombic efficiency measured in FIG. 1 as the average Coulombic efficiency. The average coulombic efficiency means a value obtained by summing the charge/discharge efficiency values for each cycle of the Li-Cu asymmetric cell and averaging over 50 cycles.

additive additive content Average Coulomb Efficiency Example 1 Pyr1(12) FSI ^{note 1 )} 30% by weight 97.4% Comparative Example 1 - 0% by weight 44.4% Comparative Example 2 Im1(4) TFSI ^{note 2 )} 29% by weight 47.9% Comparative Example 3 Im1(4) FSI ^{note 3 )} 24% by weight 77.4% Comparative Example 4 Pyr1(4) TFSI ^{Note 4 )} 29% by weight 72.9% Comparative Example 5 Pyr1(4) FSI ^{Note 5 )} 24% by weight 96.3% Note 1) Pyr1(12) FSI: 1-Dodecyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide
Note 2) Im1(4) TFSI: 1-Butyl-1-methylimidazolium bis(trifluoromethylsulfonyl)imide
Note 3) Im1(4) FSI: 1-Butyl-1-methylimidazolium bis(fluorosulfonyl)imide
Note 4) Pyr1(4) TFSI: 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide
Note 5) Pyr1(4) FSI: 1-Butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide

1 and Table 2, Example 1 uses an additive containing pyrrolidinium as the cation of the ionic liquid used as the additive and bis(fluorosulfonyl)imide as the anion, It can be seen that the coulombic efficiency does not decrease and the average coulombic efficiency is also high during 50 discharge cycles.

Experimental example 2: Battery performance according to the aliphatic chain length included in the cation of the additive

Battery performance was evaluated according to the length of the aliphatic chain included in the cation of the ionic liquid used as an additive. Experimental conditions were set to the following two conditions and each experiment was conducted.

Condition 1) 0.5 mA cm ^-2 charging / 1 mA cm ^-2 discharging condition, 300 cycles of charging and discharging

Condition 2) 1 mA cm ^-2 charge / 3 mA cm ^-2 discharge conditions, 300 cycles charge and discharge

2a and 2b are results obtained by measuring coulombic efficiencies according to charge/discharge cycles for Li-Cu asymmetric cells prepared in Example 1 and Comparative Example 5 under different charging and discharging conditions. Table 3 and Table 4 below show the Coulombic efficiency measured in FIGS. 2A and 2B as average Coulombic efficiency.

additive additive content Average Coulomb Efficiency Example 1 Pyr1(12)FSI 30% by weight 98.7% Comparative Example 5 Pyr1(4)FSI 24% by weight 96.1% Pyr1(12) FSI: 1-Dodecyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide
Pyr1(4) FSI: 1-Butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide

additive additive content Average Coulomb Efficiency Example 1 Pyr1(12)FSI 30% by weight 98.0% Comparative Example 5 Pyr1(4)FSI 24% by weight 93.6% Pyr1(12) FSI: 1-Dodecyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide
Pyr1(4) FSI: 1-Butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide

Referring to Figures 2a and 2b and Tables 2 and 4, the Coulombic efficiency of Example 1, in which the length of the aliphatic chain bound to pyrrolidinium, which is a cation of the ionic liquid included in the additive of the electrolyte, is relatively long, is excellent. Able to know. These results can be inferred that the longer the length of the aliphatic chain bonded to the pyrrolidinium, the higher the repulsive force with lithium ions on the surface of the lithium metal, thereby inhibiting the growth of lithium dendrites.

Experimental Example 3: Life characteristics of Li │ LFP full cell according to the type of additives included in the electrolyte

In order to confirm the lifespan characteristics of the battery according to the type of additives included in the electrolyte, the Li│LFP full cells prepared in Example 1, Comparative Example 1, and Comparative Example 5, respectively (lithium metal thin film as a negative electrode-LiFePO ₄ as a positive electrode) full cell) was subjected to charge/discharge life characteristics. The experimental conditions were as follows.

- LFP loading: 10 mg/cm ²

- 0.8 mA cm ^-2 charge / 0.8 mA cm ^-2 discharge, 500 cycles

Figure 3a is a graph showing the results of the charge and discharge test for the Li-LFP full cell prepared in Example 1, Comparative Example 1, and Comparative Example 5, respectively. 3B is a SEM photograph showing a cross-section of a lithium metal negative electrode after 120 cycles of charging and discharging for Li-LFP full cells prepared in Example 1, Comparative Example 1, and Comparative Example 5, respectively.

Table 3 below describes the number of cycles maintaining 80% of the maximum capacity of the Li-LFP full cell after the charge/discharge life characteristics test.

additive additive content Number of cycles maintained at 80% of peak capacity Example 1 Pyr1(12)FSI 30% by weight 294 cycles Comparative Example 1 - - 97 cycles Comparative Example 5 Pyr1(4)FSI 24% by weight 261 cycles Pyr1(12) FSI: 1-Dodecyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide
Pyr1(4) FSI: 1-Butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide

Referring to FIG. 3A and Table 4, in the case of Comparative Example 1 without using electrolyte additives, the number of cycles maintaining 80% of the maximum capacity was significantly higher than that of Example 1 and Comparative Example 5 using electrolyte additives. you can see the little things

In addition, referring to Example 1 and Comparative Example 5, the length of the aliphatic chain in which the cation of the ionic liquid included in the additive of the electrolyte is bound to pyrrolidinium is relatively long, Example 1 maintains 80% of the highest capacity It can be seen that the number of cycles is large.

Also, referring to FIG. 3B , it can be seen that in Example 1, the volume change of the lithium metal negative electrode after charging and discharging is small compared to Comparative Examples 1 and 5.

Although the present invention has been described above with limited examples and drawings, the present invention is not limited thereto, and is described below with the technical spirit of the present invention by those skilled in the art to which the present invention belongs. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be made.

Claims (8)

A lithium metal battery including a LiFePO ₄ positive electrode having a thickness of 40 μm, a lithium metal negative electrode having a thickness of 40 μm, and an electrolyte,
The electrolyte includes an organic solvent, a lithium salt and an additive,
The additive is represented by the following formula (1) as an ionic liquid,
The additive is contained by 20 to 30% by weight based on the total weight of the electrolyte, a lithium metal battery:
[Formula 1]
1-X-1-methylpyrrolidinium bis(fluorosulfonyl)imide
The X is a C ₉ to C ₁₂ alkyl group. delete delete delete delete According to claim 1,
The organic solvent is at least one lithium metal battery selected from the group consisting of ether-based solvents, ester-based solvents, amide-based solvents, linear carbonate-based solvents and cyclic carbonate-based solvents. According to claim 1,
The lithium salt is LiFSI, LiPF ₆ , LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, at least one lithium metal battery selected from the group consisting of lithium chloroborane and lithium 4-phenyl borate.

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