KR20050041093A - Electrolyte for lithium metal battery and lithium metal battery comprising same - Google Patents

Abstract

The present invention relates to a lithium metal battery electrolyte and a lithium metal battery comprising the same, the lithium metal battery electrolyte is an additive capable of forming a polymer film on the surface of the negative electrode by electrochemical reduction; Non-aqueous organic solvents; And lithium salts.

The electrolyte additive for a lithium metal battery according to the present invention forms a protective film by polymerizing an additive on a lithium metal negative electrode surface in a battery, and the formed protective film improves stability of the lithium metal negative electrode to improve cycle life. In addition, when the electrolyte additive according to the present invention is added to a lithium sulfur battery, a protective film of the lithium metal negative electrode is used to suppress not only the cycle life of the lithium metal battery but also the shuttle phenomenon caused by the reaction between the lithium polysulfide and the lithium metal during charging. Efficient charging was possible and the charging and discharging efficiency and discharge capacity could be increased.

Description

ELECTROLYTE FOR LITHIUM METAL BATTERY AND LITHIUM METAL BATTERY COMPRISING SAME

[Industrial use]

The present invention relates to a lithium metal battery electrolyte and a lithium metal battery comprising the same, and more particularly to a lithium metal battery electrolyte and a lithium metal battery comprising the same, which can provide a battery having excellent cycle life characteristics and high discharge capacity. It is about.

[Prior art]

BACKGROUND With the rapid development of the electrical, electronic, telecommunications and computer industries, the demand for high performance and high safety secondary batteries has recently increased rapidly. In particular, secondary batteries, which are key components, are also required to be lighter in weight and smaller in size, due to light and short and portable trends of electric and electronic products. In addition, the necessity of the development of electric vehicles that can solve this problem has been increased as the need for a new type of energy supply and demand due to the exhaustion of oil and environmental pollution, such as air pollution and noise, due to the mass distribution of automobiles As a result, development of batteries having high power and high energy density has been demanded.

In response to such demands, one of the latest high-performance, next-generation high-tech batteries that has received the most attention recently is a lithium metal battery (LMB). A lithium metal battery is a battery which uses lithium metal as a negative electrode, and can mention a lithium ion battery and a lithium sulfur battery largely. Lithium, which is used as a negative electrode, is the most popular electrode material for high energy density batteries because of its low density of 0.54 g / cm ³ and a very low standard reduction potential of -3.045 V Standard Hydrogen Electrode (SHE). However, when using lithium metal as a negative electrode has not yet been practical due to the following problems.

First, when lithium metal is used as a negative electrode of an ion battery, lithium metal reacts with impurities such as electrolyte, water or organic solvent, lithium salt, and the like to form a passivation layer (SEI: Solid Electrolyte Interphase). It causes a difference in current density to promote the formation of dendritic dendrites by lithium metal during charging, and gradually grows during charging and discharging, causing an internal short circuit between the positive electrode and the negative electrode. In addition, dendrite has a mechanically weak neck, which forms dead lithium, which loses electrical contact with the current collector during discharge, thereby reducing battery capacity and reducing cycle life and stability of the battery. Adversely affects. Due to the heterogeneity of the redox reaction of the lithium cathode and the reactivity with the electrolyte, lithium metal ion batteries have not been commercialized yet.

In addition, when lithium metal is used as a negative electrode of a lithium sulfur battery, a shuttle mechanism in which lithium polysulfide and a lithium negative electrode reacted and reduced during the charging and discharging process is expressed, so that the positive electrode material cannot obtain a high charge rate. This has a problem of limiting the discharge capacity of the lithium sulfur battery. The lithium polysulfide is produced by electrochemical reduction in the 2.4V region when the sulfur, which is the cathode active material of the sulfur battery, is discharged, or a solid reducing product of lithium disulfide and lithium sulfide is formed on the surface of the carbon matrix mixed in the positive electrode in the 2V region. These are again produced by oxidation with lithium polysulfide.

The reaction between the lithium polysulfide and the lithium metal may dissolve lithium polysulfide in an electrolyte solution and diffuse to the lithium metal anode, and a passivation layer formed on the surface of the lithium cathode may be broken during charging and discharging, thereby increasing the activity of lithium. bare Li) is exposed. The reaction between the lithium polysulfide and the lithium metal causes not only low charging efficiency but also a problem of causing spontaneous discharge during battery storage after charging.

In order to solve the problem of reaction between lithium metal and electrolyte and the formation of dendrite, U.S. Patent No. 4,002,492 proposes a method of using lithium aluminum alloy as a negative electrode, but the capacity drop and mechanical properties are brittle and discharge potential Is lowered, and the specific capacity of the negative electrode is reduced. U. S. Patent No. 6,537, 702 describes a structure in which a lithium aluminum alloy protective film containing Al ₂ S ₃ is located on the surface of a lithium metal and mentions its application to a lithium sulfur battery.

U.S. Patent No. 4,503,088 uses an epoxy resin solution coated on a lithium metal negative electrode as a protective film, but the solvent in the solution is likely to directly contact the lithium metal to form a side reaction, and there is a problem that bubbles are generated at the interface. In addition, US Patent No. 4,359,818 used a method of manufacturing a protective film in the form of a thin film to solve this problem, and then put it on a lithium metal to press and bond, but this method is difficult to manufacture and handle the film of the thin film There is a disadvantage that the material constituting the protective film must have a sufficiently high ion conductivity.

U.S. Patent No. 4,934,306 overcomes the difficulties in handling and manufacturing thin films by using a method of coating and drying a protective film solution on a porous film and pressing and bonding to a lithium metal. There is a problem that is difficult to block.

U.S. Pat.Nos. 5,342,710, 5,487,959 and 5,342,710 use the complex of I ₂ and poly- ₂ -vinylpyridine as a protective film, and the added I ₂ reacts with lithium metal to form LiI, thereby protecting the lithium metal. However, there is a problem that the ion conductivity is lowered and the interface stability is lowered.

U. S. Patent No. 5,961, 672 uses a vacuum-deposited electroconductive coating as a protective film for a lithium metal anode, but since the work is performed under high vacuum, the process is complicated and expensive, and the type of monomer that can be used in the vacuum deposition method It is limited and the production rate is slow because the deposition rate is not high.

US Pat. Nos. 6,214,061 and 6,432,584 have prepared a protective film of a lithium cathode by depositing an inorganic monoion conductor on the surface of a lithium metal anode. The protective film prepared in this way has a problem that cracks are generated during repeated reactions on the lithium surface due to the weak mechanical strength of the inorganic material, and the production speed is slow due to the low speed of the deposition process. On the other hand, US Patent No. 5,314,765 was prepared by depositing a multi-layer inorganic mono-ion conductor on the surface of the lithium metal cathode to prepare a lithium cathode protective film. However, such a multilayer inorganic protective film also has a low mechanical strength is easy to break the protective film, there is a problem of low productivity of the multilayer deposition process.

Lithium thionyl chloride battery, a lithium primary battery, has been reported for stabilization of a lithium metal negative electrode. According to US Patent Nos. 4,503,088 and 4,359,818, alkyl acrylates, alkyl substituted acrylates, and alkylcyanoacrylate-based polymers have been reported. It was applied over lithium to form a protective film.

According to Korean Patent Publication No. 2003-42288, a protective film was formed by applying a mixed solution of an electrolyte component, a crosslinkable monomer, and an initiator on a lithium negative electrode, and then applying UV or heat. In this way, the reaction between the electrolyte and lithium was reported to be reduced. However, since the protective film described in the patent has a liquid protective film component is applied to lithium, in order to form a uniform protective film on the lithium surface through a continuous process, the crosslinking reaction of the protective film component should be performed immediately after the coating on the lithium metal foil. Fairness depends on the reaction time. In addition, as the crosslinking reaction of the protective film proceeds, the protective film becomes harder and more fragile, which causes a problem that the protective film is broken by volume change of the lithium surface during charging and discharging. However, when the crosslinking reaction of the protective film is reduced, the protective film is ductile, but swelling is caused by the electrolyte when contacted with the electrolyte, and when the swelling is severe, the protective film is peeled off from lithium and wrinkles are formed. In addition, since the protective film contains an excessive amount of electrolyte components, the reaction between the electrolyte and lithium continues to occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to suppress dendrite growth occurring on the surface of lithium metal during charging and discharging of a battery, and to prevent lithium metal from reacting with a lithium metal anode, an electrolyte, and a cathode active material. It is to provide a lithium metal battery electrolyte solution that can suppress the loss to improve the life.

Another object of the present invention is to provide a lithium metal battery containing the electrolyte solution.

In order to achieve the above object, the present invention is an additive capable of forming a polymer film on the surface of the cathode by electrochemical reduction; Non-aqueous organic solvents; And it provides a lithium metal battery electrolyte solution containing a lithium salt.

The present invention also provides an electrolyte comprising an additive, a non-aqueous organic solvent and a lithium salt which can form a polymer film on the surface of the cathode by electrochemical reduction; A positive electrode including a positive electrode active material; And a negative electrode of a lithium metal or a lithium alloy.

Hereinafter, the present invention will be described in more detail.

The present invention relates to an electrolyte solution involved in forming a protective film on a negative electrode of a lithium metal battery. A lithium metal battery is a battery using lithium metal as a negative electrode and can be broadly classified into a lithium ion battery and a lithium sulfur battery. Of course, batteries that use lithium alloys instead of lithium metals are also included. Since the standard reduction potential of lithium metal is -3.04V and has the lowest reduction potential among solid negative electrode active materials, it is a material that can exhibit the highest potential of the battery when used as a negative electrode. In addition, lithium metal has a capacity per unit weight of 3860mAh / g and is the largest active material per unit weight of the known material so far. Therefore, when lithium metal is used in a battery, it is the most suitable material for producing a light and high capacity battery.

However, when lithium metal is used in an ion battery, needle-shaped lithium called dendrite is formed on the surface of the lithium negative electrode, and when such dendrites grow excessively and contact the positive electrode, an internal short circuit occurs. These dendrites are oxidized to lithium ions when lithium metal is discharged, and during charging, the lithium ions are reduced on the surface of lithium metal to precipitate as lithium, that is, the volume of the surface of lithium metal by redox reaction of lithium metal. Changes occur, so that precipitation of lithium during charging is generally not uniform, but rather concentrated and formed. In addition, lithium metal is highly reactive with the electrolyte component, and when the electrolyte component is in contact with the lithium metal, a spontaneous reaction forms a film called a passivation layer. The protective film formed on the surface of lithium during charge and discharge repeats destruction and formation. Therefore, when the battery is repeatedly charged and discharged, the protective film component in the lithium negative electrode increases and the problem of depletion of the electrolyte occurs. Due to the reaction between the electrolyte and the dendrite, the dendrite may be electrically shorted with the lithium metal. Such lithium is called 'dead lithium' and does not participate in the electrochemical reaction. do.

 In addition, in the lithium sulfur battery, a shuttle mechanism in which lithium polysulfide formed during charge / discharge of the positive electrode active material reacts with lithium in the lithium metal negative electrode is reduced, resulting in a high charge rate. This limits the discharge capacity of the lithium sulfur battery, and the reaction between lithium polysulfide and lithium metal causes not only low charging efficiency, but also causes a problem of spontaneous discharge during battery storage after charging.

In the present invention, in order to solve the problem of the lithium metal to provide a high capacity lithium metal battery using a lithium metal as a negative electrode, after mixing the additive to form a stable protective film on the surface of the lithium negative electrode in an electrolyte solution to prepare a battery, By the conditions, a stable protective film was formed on the lithium metal surface. Even when the protective film is broken during charging and discharging of the battery, a healing effect may be provided to form a protective film again on the exposed lithium surface of the additive remaining in the electrolyte. The protective film formed by the additive blocks the reaction between the soluble positive electrode active material such as electrolyte and lithium polysulfide and lithium, thereby improving the life of the lithium negative electrode and increasing the charging efficiency of the positive electrode active material, thereby obtaining a high discharge capacity.

In general, the characteristics of the lithium metal protective film varies greatly depending on the type of electrolyte. When the protective film is porous, the reaction between the electrolyte and lithium continues to occur, resulting in a thickness of several microns. On the other hand, when the protective film is dense, the contact between the electrolyte and lithium is blocked, thereby suppressing the continuous growth of the protective film. Therefore, in order to improve the performance of the lithium anode, dendrite formation should be suppressed on the surface of lithium, and the reaction between the electrolyte and lithium should be minimized to prevent depletion of the electrolyte and formation of inert lithium.

One of the characteristics of the protective film of the lithium metal anode to prevent this is mechanical strength to suppress the growth of dendrites. Local concentration of lithium should be excellent in the mechanical strength of the protective film when the dendrite is grown, and the growth of the dendrite in the vertical direction of the protective film should be suppressed. Since the protective film made of an inorganic material has a low toughness and may cause a problem in that the protective film is broken due to the volume change of the lithium metal surface by lithium precipitation, the protective film preferably has a high strength polymer component. In addition, the protective film should have excellent adhesion with lithium metal. When the adhesion is low, when the volume of the lithium metal surface changes, the interface between the lithium metal and the protective film is peeled off, and the protective film loses its function. In addition, the protective film should be able to effectively block the electrolyte. For this purpose, the protective film should have a low degree of swelling in the electrolyte.

The electrolyte solution of the present invention includes at least one additive that can form a polymer film on the surface of the cathode by electrochemical reduction. The additive is preferably a compound having at least one double bond, and the standard reduction potential is preferably in the range of -1.5 to -3.04V, more preferably -1.5 to -3.0V.

The first form of the additive of the present invention is a material for forming a polymer film on the surface of lithium by electrochemical reduction at the lithium cathode. The additive has an intramolecular double bond structure, and may form anion radicals while receiving and reducing electrons when charging a battery on a lithium metal negative electrode surface. These anionic radicals react with additives with surrounding double bonds to polymerize by radical polymerization or anionic polymerization mechanisms, which are insoluble in electrolytes and form on the surface of lithium anodes. Will be. When the polymer film is grown to a certain thickness or more, the additive cannot diffuse to the lithium metal so that the polymerization reaction is terminated, and a protective film of a constant thickness remains on the lithium surface. This reactor is shown in Scheme 1 below.

Scheme 1

(Wherein X is a functional group bonded to a double bond in the additive usable in the present invention, n is an integer from 2 to 1,000,000)

The second form of the additive of the present invention has an intramolecular double bond structure, and when it encounters lithium metal, it can form an anion radical while being reduced by a chemical reaction. This is because the additive having a double bond structure has a higher reduction potential than lithium and can be reduced without supplying electrons from the outside. This reaction occurs not only during charging and discharging, but also during storage, and a protective film formed on the surface of the lithium negative electrode is broken to react with the exposed lithium negative electrode. Anionic radicals formed by reaction with lithium are reacted with additives with surrounding double bonds to be polymerized by radical polymerization or anionic polymerization mechanisms, and these polymers are insoluble in the electrolyte. It is then formed on the surface of the lithium anode. When the polymer film is grown to a certain thickness or more, the additive cannot diffuse to the lithium metal so that the polymerization reaction is terminated and a protective film of a certain thickness remains on the lithium surface. This reaction mechanism is shown in Scheme 2 below.

Scheme 2

(Wherein X is a functional group bonded to a double bond in the additive usable in the present invention, n is an integer from 2 to 1,000,000)

The third form of the additive of the present invention has an intramolecular double bond structure, and when it meets with lithium metal, it provides electrons to the cathode during discharge and can form cationic radicals while being oxidized. The cationic radicals are polymerized by radical polymerization or cationic polymerization by reacting with additives having surrounding double bonds, which are insoluble in the electrolyte and are formed on the surface of the lithium negative electrode. When the polymer film is grown to a certain thickness or more, the additives do not diffuse and penetrate the film, so that the reaction is terminated and a protective film of a certain thickness remains on the lithium surface. This reaction mechanism is shown in Scheme 3 below.

Scheme 3

(Wherein X is a functional group bonded to a double bond in the additive usable in the present invention, n is an integer from 2 to 1,000,000)

Preferred examples of the additive of the present invention include compounds having at least one acrylic group. Examples of the compound having one or more acrylic groups include alkyl acrylate, alkyldiol diacrylate, polyethylene oxide diacrylate, polymethylene oxide diacrylate, polypropylene oxide diacrylate, polytetrafluoroethylene diacrylate, Acrylic acid, acrylamide or acrylonitrile.

Other preferred examples of the additives of the present invention include compounds having one or more substituted acrylic groups. Examples of this compound include alkyl methacrylates, alkyl butacrylates, alkyldiol dimethacrylates, polyethylene oxide dimethacrylates, polymethylene oxide dimethacrylates, polypropylene oxide dimethacrylates, polytetrafluoroethylene Dimethacrylate, methacrylic acid, methacrylamide or methacrylonitrile.

Other preferred examples of the additives of the present invention include compounds having one or more allene groups. Examples of this compound include allene or allenyl tributytiltin.

Other preferred examples of the additives of the present invention include compounds having one or more allyl groups. Examples of this compound include allyl acetate, allyl alcohol, allyl alcohol propoxylate, allylamine, allylaniline, allylanisole, allylbenzene or allyl bromide.

Other preferred examples of the additives of the present invention include compounds having one or more cinnamate groups. Examples of this compound include cinnamic acid, alkylsanimate, vinyl cinnamate, cinnamil acetate, cinnamil alcohol, cinnamil bromide or cinnamil chloride.

Other preferred examples of the additives of the present invention include compounds having one or more acryloyl groups. Examples of this compound include acryloyl chloride.

Other preferred examples of the additives of the invention include compounds having one or more substituted acryloyl groups. Examples of this compound include methacryloyl chloride or butacryloyl chloride.

Another preferred example of the additive of the present invention includes a compound having a vinyl group. Examples of this compound include vinyl chloride, trivinyl fluoride, tetravinyl fluoride, vinyl fluoride, trivinyl fluoride or tetravinyl fluoride.

Another preferred example of the additive of the present invention includes a compound having a vinylidene group. Examples of this compound include vinylidene fluoride, vinylidene chloride, vinylidene carbonate, vinylidene sulfide or vinylidene bromide.

Another preferred example of the additive of the present invention includes a compound having a styrene group. Examples of this compound include styrene, substituted styrene, styrenecarboxylic acid or styrenesulfonic acid.

Another preferred example of the additive of the present invention includes a compound having an itaconic group. Examples of this compound include itaconic acid, itaconic chloride or itaconic anhydride.

The content of the additive in the electrolyte solution of the present invention is preferably 0.01 to 5% by weight, more preferably 0.1 to 2% by weight. When the content of the additive is lower than 0.01% by weight, the amount of lithium cathode film formation by the additive is low and its effect is insignificant. When the content of the additive is more than 5% by weight, the film is formed too thick to increase the resistance of the battery. The problem that the resistance of the battery increases due to the increase occurs is undesirable.

The electrolyte solution of the present invention comprising the additive also includes a non-aqueous organic solvent and a lithium salt.

As this non-aqueous organic solvent, a single solvent may be used or two or more mixed organic solvents may be used. When using two or more mixed organic solvents, it is preferable to select one or more solvents from two or more groups among the weak polar solvent group, the strong polar solvent group, and the lithium metal protective solvent group.

Weak polar solvents are defined as those having a dielectric constant of less than 15 that can dissolve elemental sulfur among aryl compounds, bicyclic ethers, and acyclic carbonates; strong polar solvents include acyclic carbonates, sulfoxide compounds, lactone compounds, Among ketone compounds, ester compounds, sulfate compounds, and sulfite compounds, a dielectric constant capable of dissolving lithium polysulfide is defined as greater than 15, and lithium protective solvents are saturated ether compounds, unsaturated ether compounds, N, O, It is defined as a solvent having a charge and discharge cycle efficiency (cycle efficiency) of 50% or more to form a SEI (Solid Electrolyte Interface) film stable on lithium metal, such as a heterocyclic compound containing S or a combination thereof.

 Specific examples of weak polar solvents include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme, tetraglyme and the like.

Specific examples of strong polar solvents include hexamethyl phosphoric triamide, gamma-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone , Dimethyl formamide, sulfolane, dimethyl acetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, or ethylene glycol sulfite.

Specific examples of the lithium protective solvent include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethyl isoxazole, 2,5-dimethyl furan, furan, 2-methyl furan, 1,4-oxane, 4-methyldioxolane Etc.

The electrolytic salt lithium salt is lithium trifluoromethansulfonimide (lithium trifluoromethansulfonimide), lithium triflate (lithium triflate), lithium perchlorate (lithium perclorate), LiPF ₆ , LiBF ₄ or tetraalkylammonium, for example tetra One or more butylammonium tetrafluoroborate, or liquid salts at room temperature, such as imidazolium salts such as 1-ethyl-3-methylimidazolium bis- (perfluoroethyl sulfonyl) imide and the like Can be.

The lithium secondary battery including the electrolyte solution of the present invention includes a positive electrode and a negative electrode. As the cathode active material in the cathode, elemental sulfur (S ₈ ), a sulfur-based compound, or a mixture thereof may be used. The sulfur compound is Li ₂ S _n (n≥1), polysulfide (Li ₂ S _x , x≥2), 2,5-dimercapto-1,3,4-thiadiazole (DMct, 2,5 disulfide compounds, organic sulfur compounds and carbon-sulfur polymers, including -dimercapto-1,3,4-thiadiazole) or 1,3,5-trithiocyanuic acid (TTCA, 1,3,5-trithiocyanuic acid) ((C ₂ S _x ) _n : x = 2.5 to 50, n ≥ 2) can be selected from the group consisting of. In addition, a lithium transition metal oxide capable of reversibly intercalating and deintercalating lithium commonly used in a lithium ion battery may also be used.

The negative electrode may be selected from the group consisting of lithium metal and lithium alloy as the negative electrode active material. As the lithium alloy, an alloy of a metal selected from the group consisting of lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn may be used.

An inorganic protective layer, an organic protective layer, or a material in which these layers are stacked on a lithium metal surface may also be used as a cathode. As the inorganic protective film, Mg, Al, B, C, Sn, Pb, Cd, Si, In, Ga, lithium silicate, lithium borate, lithium phosphate, lithium phosphoronide, lithium silicon sulfide, lithium borosulfide, lithium aluminium It consists of a material selected from the group consisting of nosulfide and lithium phosphosulfide. The organic protective film is poly (p-phenylene), polyacetylene, poly (p-phenylene vinylene), polyaniline, polypyrrole, polythiophene, poly (2,5-ethylene vinylene), acetylene, poly (ferry) Naphthalene), polyacene, and poly (naphthalene-2,6-diyl), and a monomer, oligomer or polymer having conductivity selected from the group consisting of.

In addition, a separator for preventing a short circuit between the positive electrode and the negative electrode in the lithium secondary battery may be included, and such a separator may be a polymer film such as polypropylene or polyethylene, or a multilayer thereof.

The lithium secondary battery including the electrolyte, the positive electrode, the negative electrode, and the separator described above has a unit cell having a structure of positive electrode / separator / cathode, a bicell having a structure of positive electrode / separator / cathode / separator / anode, or a unit cell structure. It can be formed in the structure of a repeated laminated battery. The electrolyte solution is injected into the battery container containing the structure is present. The electrolyte solution of the present invention may be used as a liquid electrolyte solution, or may be used as a polymer electrolyte depending on materials and methods used in the manufacture of conventional polymer electrolytes.

A representative example of the lithium secondary battery of the present invention having such a configuration is shown in FIG. 1. 1 includes a positive electrode 2, a negative electrode 3, and a separator 4 positioned between the positive electrode 2 and the negative electrode 3, and an electrolyte solution between the positive electrode 2 and the negative electrode 3. The rectangular type lithium ion battery 1 including the case 5 in which the figure is shown is shown. Of course, the lithium secondary battery of the present invention is not limited to this shape, it is natural that any formation such as cylindrical, pouch, etc., including the positive electrode active material of the present invention and can operate as a battery.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Comparative Example 1)

Lithium deposited to a thickness of 15 micron on a copper current collector using a cathode, a 100 micron lithium foil as a counter electrode, a porous polyethylene separator of 16 micron is placed between the anode and the counter electrode, and a plastic pouch coated with aluminum A lithium half cell was prepared. At this time, 1M LiN (CF ₃ SO ₂ ) ₂ dimethoxyethane / diglyme / dioxolane (4/4/2 by volume) was injected into the electrolyte solution. The battery was charged and discharged at a current density of 1 mA / cm ² for 2 hours. The change in battery voltage according to charge and discharge is shown in FIG. 2. During discharge, a precipitation reaction of lithium occurs at the anode and a stripping reaction of lithium occurs at the counter electrode. The battery voltage at discharge was -100 mV. During charging, the stripping reaction of lithium at the positive electrode showed the precipitation reaction of lithium at the negative electrode. The battery voltage was 100 mV at the time of charging. In the seventh charge, the cell's voltage rises to 1.7V, which means that the lithium in the anode is completely exhausted in seven cycles due to the continuous exhaustion of lithium at the anode. In this case, the coulombic efficiency of the electrolyte was 63.9% and the figure of Merit (FOM) was 2.77.

(Example 1)

Lithium half cell using lithium deposited with a thickness of 15 micron on a copper current collector as a positive electrode, a 100 micron lithium foil as a counter electrode, a 16 micron porous polyethylene separator between the positive electrode and the counter electrode, and an aluminum-coated plastic pouch. Was prepared. In this case, 5% by weight of hexanediol diacrylate was added to dimethoxyethane / diglyme / dioxolane (4/4/2 by volume) in which 1M LiN (CF ₃ SO ₂ ) ₂ was dissolved. . The prepared battery was charged and discharged at a current density of 1 mA / cm ² for 2 hours, and the change in battery voltage according to charging and discharging is shown in FIG. 3. In the initial discharge, the battery voltage is formed at −1 V lower than that of Comparative Example 1 containing no additive, and the battery voltage is formed at 1 V higher than that of Comparative Example 1 containing no additive during initial charging. This means that when the additive is contained, the reduction reaction of the additive occurs in the positive electrode during discharging and the dissolution of lithium occurs in the counter electrode. In addition, it means that the reduction reaction of the additive occurs in the counter electrode during charging and the reduction reaction of lithium occurs in the positive electrode. In the case of the electrolyte containing additives, the Coulomb efficiency was 93.8% and the FOM was 16.05. This shows that the polymer film of the additive in the lithium surface formed during the initial charge and discharge stabilized the lithium anode.

(Example 2)

Except for the addition of 3% by weight of vinyl cinnamate to dimethoxyethane / diglyme / dioxolane (4/4/2 by volume) in which 1M LiN (CF ₃ SO ₂ ) ₂ was dissolved It carried out similarly to Example 1 above. The prepared half battery was charged and discharged at a current density of 1 mA / cm ² for 2 hours. In the case of the electrolyte containing additives, the coulombic efficiency was improved to 97.1% and the FOM to 35. This shows that the polymer film of the additive in the lithium surface formed during the initial charge and discharge stabilized the lithium cathode.

(Example 3)

As in Example 1, except that 4% by weight of acrylic acid was added to dimethoxyethane / dioxolane (4/6 vol. Ratio) in which 0.5M LiN (CF ₃ CF ₂ SO ₂ ) ₂ was dissolved. Was carried out. The prepared half battery was charged and discharged at a current density of 1 mA / cm ² for 2 hours. In the case of the electrolyte solution containing the additive, the Coulomb efficiency was 98.0% and the FOM was 52.3.

(Example 4)

A dimethoxyethane / diglyme / dioxolane (4/4/2 volume ratio) in which 1M LiN (CF ₃ SO ₂ ) ₂ was dissolved was used, using an electrolyte solution containing 2% by weight of acrylonitrile and 1% by weight of acrylic acid. Except that was carried out in the same manner as in Example 1. The prepared half battery was charged and discharged at 1 mA / cm ² for 2 hours. In the case of the electrolyte solution containing the additive, the coulombic efficiency was 98.3% and the FOM was 60.3.

(Comparative Example 2)

The same procedure as in Example 1 was carried out except that dimethoxyethane / dioxolane (9/1 volume ratio) electrolyte in which 0.8 M Li ₂ S ₈ was dissolved was used. The prepared half battery was charged and discharged at a current density of 1 mA / cm ² for 2 hours. Coulomb efficiency was 24.4% and FOM was 1.32.

(Example 5)

0.8M Li ₂ S _8, except the dissolved dimethoxyethane / dioxolane (9/1 volume ratio) that the used electrolytic solution was added to 4% by weight of acrylonitrile on acrylate was performed in the same manner as in the Comparative Example 2. The prepared half battery was charged and discharged at a current density of 1 mA / cm ² for 2 hours. In the case of the electrolyte solution containing the additive, the Coulomb efficiency was 97.2% and the FOM was 35.3. This is a 3.98-fold increase in coulombic efficiency and a 26.7-fold increase in FOM compared with no additives.

(Example 6)

The same procedure as in Comparative Example 2 was performed except that an electrolyte solution containing 5% by weight of hexanediol diacrylate was added to dimethoxyethane / dioxolane (9/1 vol. Ratio) in which 0.8 M Li ₂ S ₈ was dissolved. . The prepared half battery was charged and discharged at a current density of 1 mA / cm ² for 2 hours. In the case of the electrolyte solution containing the additive, the Coulomb efficiency was 96.4% and the FOM was 30.8.

(Comparative Example 3)

A positive electrode of a lithium sulfur battery having a capacity of ² mAh / cm ² was prepared in a conventional manner using 75 wt% inorganic sulfur (S ₈ ), 15 wt% carbon conductive material, and 10 wt% polyethylene oxide binder. A wound lithium sulfur battery was manufactured using the positive electrode and the lithium metal foil negative electrode of 60 micron. The theoretical capacity of the prepared battery was 1000 mAh, and the electrolyte solution used was dimethoxyethane / diglyme / dioxolane (4/4/2 by volume) in which 1M LiN (CF ₃ SO ₂ ) ₂ was dissolved.

Charge and discharge of the manufactured lithium sulfur battery with charging / discharging speeds of 0.5C / 0.2C, discharge limit potential of 1.5V, and charging at 750mAh capacity cut-off or 3.5V charge limit potential, respectively. The charge and discharge efficiency and capacity according to the charge and discharge cycle was measured and the results are shown in Table 1 below. The charge / discharge efficiency represents discharge capacity / charge capacity.

1 time Episode 2 5 times 10th 50 times 100 times Volume 700 mAh 480 mAh 470 mAh 400 mAh 120 mAh - Charge and discharge efficiency - 64% 62.7% 53.3% 16.0% - Charging end voltage 2.42 V 2.43V 2.45V 2.45V 2.46V -

As shown in Table 1, the charging and discharging efficiency is very low because the oxidation degree of the active material is not increased by a shuttle phenomenon in which lithium polysulfide oxidized at the anode during charging is reduced by chemical reaction with the lithium anode. It can be seen. In addition, since the shuttle phenomenon occurs during charging, the oxidation degree of the anode does not increase, so the terminal voltage at the end of charging is maintained in the 2.4V region.

(Example 7)

An electrolyte solution in which 5% by weight of hexanediol dimethacrylate was added to a mixed solvent of dimethoxyethane / diglyme / dioxolane (4/4/2 volume ratio) in which 1M LiN (CF ₃ SO ₂ ) ₂ was dissolved was used. Except that was carried out in the same manner as in Comparative Example 3.

The prepared lithium sulfur battery was charged and discharged under the same conditions as in Comparative Example 3 to measure charge and discharge efficiency and capacity according to charge and discharge cycles, and the results are shown in Table 2 below.

1 time Episode 2 5 times 10th 50 times 100 times Volume 695 mAh 680 mAh 682 mAh 678 mAh 659 mAh 605 mAh Charge and discharge efficiency - 90.7 90.9 90.4 95.2 96.2 Charging end voltage 2.95 V 3.12V 3.15V 3.2 V 3.5 V 3.5 V

As shown in Table 2, it can be seen that the battery of Example 7 has improved cycle life and increased discharge capacity after two times compared to Comparative Example 3. This is because the coating of the additives in the lithium surface formed during the initial charge and discharge inhibited the reaction between lithium and the lithium polysulfide in solution, and thus the active material was effectively oxidized during charging, and as a result, the discharge capacity and the charge and discharge efficiency were thought to be improved. In addition, the shuttle reaction was inhibited by the protective film, and as the oxidation degree of the active material in the positive electrode increased at the end of charge, the voltage was continuously increased, and the charge termination voltage was greatly increased as compared with Comparative Example 3, and as the cycle progressed, the charge termination voltage was increased. It can be seen that steadily rose. This result indicates that the lithium metal surface coating is more effectively formed as the cycle progresses. In addition, it can be seen that the concentration of the local reaction of the lithium negative electrode was alleviated by the formation of a film by the additive, and the loss of lithium due to the reaction between the electrolyte and the active material and the lithium metal negative electrode was suppressed.

(Example 8)

Except for using an electrolyte solution in which 3 wt% acrylonitrile was added to a dimethoxyethane / diglyme / dioxolane (4/4/2 volume ratio) mixed solution in which 1M LiN (CF ₃ SO ₂ ) ₂ was dissolved. It carried out similarly to the comparative example 3. Charge and discharge of the prepared lithium sulfur battery under the same conditions as in Comparative Example 3, the capacity and charge and discharge efficiency according to the charge and discharge cycle was measured and the results are shown in Table 3 below.

1 time Episode 2 5 times 10th 50 times 100 times Volume 680 mAh 700 mAh 705 mAh 702 mAh 691 mAh 615 mAh Charge and discharge efficiency - 93.3 94.0 93.6 93.1 95.5 Charge termination voltage 3.15V 3.2 V 3.28 V 3.45V 3.5 V 3.5 V

As shown in Table 3, the battery of Example 8 has improved cycle life and increased discharge capacity after two times compared to Comparative Example 3. This is because the film of the additive in the lithium surface formed during the initial charge and discharge inhibits the reaction between lithium and the lithium polysulfide in solution, and the active material is effectively oxidized during charging, and as a result, the discharge capacity and the charge and discharge efficiency are considered to be improved. In addition, it can be seen that the concentration of the local reaction of the lithium negative electrode was alleviated by the formation of the film by the additive, and the loss of lithium due to the reaction between the electrolyte and the active material and the lithium metal negative electrode was suppressed.

(Example 9)

The lithium sulfur battery prepared in Example 7 was discharged after going through 20 cycles with 5% depth of discharge and 5% depth of charge at a charge and discharge rate of 1C. Repeated charging and discharging were performed under the conditions of speed and charge rate of 0.5C and 0.2C, discharge limit voltage of 1.5V and charge limit voltage of 3.5V. Capacity and charge and discharge efficiency according to this charge and discharge cycle was measured and the results are shown in Table 4 below.

1 time Episode 2 5 times 10th 50 times 100 times Volume 705 mAh 700 mAh 702 mAh 698 mAh 692 mAh 658 mAh Charge and discharge efficiency - 96.7 97.9 97.4 97.2 98.2 Charging end voltage 3.5 V 3.5 V 3.5 V 3.5 V 3.5 V 3.5 V

As shown in Table 4, as the cycle progressed to a low charge / discharge depth in the initial chemical conversion process, the charge and discharge efficiency could be increased by forming a film by an additive on the lithium metal surface.

(Comparative Example 4)

A lithium half cell was prepared using 60 micron lithium metal as the positive electrode and 200 micron lithium foil as the negative electrode. In this case, an electrolyte solution in which 3% by weight of hexanediol diacrylate was added to the electrolyte solution used in Example 1 was used. The prepared lithium half battery was charged and discharged at a current density of 4 mA / cm ² for 1 hour, and a charge and discharge curve is shown in FIG. 3. As shown in FIG. 3, 11 cycles were performed, in which case the FOM and Coulomb efficiencies were 3.3 and 69.4%, respectively.

(Example 10)

A lithium half cell was manufactured by using a 60 micron lithium metal as a positive electrode, a 200 micron lithium foil as a negative electrode, a 16 micron porous polyethylene separator between the positive electrode and the negative electrode, and using a plastic pouch coated with aluminum. At this time, an electrolyte solution in which 3% by weight of hexanediol diacrylate was added to the electrolyte solution used in Comparative Example 1 was used. The prepared lithium half cell was charged and discharged at a current density of 4 mA / cm ² for 1 hour, and the charge and discharge curves are shown in FIG. 5. As shown in FIG. 5, 43 cycles were performed, in which case the FOM and Coulomb efficiencies were 13.8 and 92.8%, respectively. This is a FOM and Coulomb efficiency 4.18 times 1.34 times increased compared with the comparative example 4, respectively.

(Comparative Example 5)

A lithium sulfur battery was constructed by using 60 micron of lithium metal as a negative electrode and a sulfur positive electrode having a capacity of ² mAh / cm ² . The electrode area was 500 cm ² and the electrolyte solution used in Comparative Example 1 was used. Symbol A in Fig. 6 shows the 15th cycle in the 0.5C discharge 0.2C charge of the battery prepared by Comparative Example 5.

(Example 11)

A lithium sulfur battery was constructed by using 60 micron of lithium metal as a negative electrode and a sulfur positive electrode having a capacity of ² mAh / cm ² . An electrode area of 500 cm ² and a dimethoxyethane / dioxolane (4/1 volume ratio) electrolyte in which 1 M lithium salt (trade name: HQ115, 3M company) was dissolved was used. Symbol B in Fig. 6 shows the 15th cycle in the 0.5C discharge 0.2C charge of the battery prepared in Example 11. In the case of Example 11 to which 5% by weight of hexanediol diacrylate was added, a higher capacity was shown because the flat portion of 2.4V was larger than that of Comparative Example 5. Example 11 also shows a higher charging potential at the end of charging, which prevents the reaction between the polysulfide, which is an active material dissolved in the electrolyte, and the lithium cathode due to the protective film formed on the lithium anode, thereby preventing the active material charged from the positive electrode. It can be confirmed that it suppresses self-discharge by reaction with metal.

(Example 12)

A lithium sulfur battery was constructed by using 200 micron of lithium metal as a cathode and a sulfur anode having a capacity of ² mAh / cm ² . The electrode area is 12.5 cm ² . An electrolyte solution in which 2% by weight of acrylic acid was added to a dimethoxyethane / dioxolane (4/1 volume ratio) electrolyte in which 1 M lithium salt (trade name: HQ115, 3M company) was dissolved was used. Figure 7 shows the initial two cycles of 0.2C discharge 0.2C charge of the battery produced. It can be seen that when the first charge is charged up to 3.5V, the shuttle reaction is suppressed, and the flat portion of the 2.4V region is clearly shown in the second discharge. This is because the film formed by the reaction of the added acrylic acid and the lithium cathode suppresses the reaction between lithium polysulfide and lithium, thereby exhibiting the effect of suppressing the shuttle.

The electrolyte additive for a lithium metal battery according to the present invention forms a protective film by polymerizing an additive on a lithium metal negative electrode surface in a battery, and the formed protective film improves stability of the lithium metal negative electrode to improve cycle life. In addition, when the electrolyte additive according to the present invention is added to a lithium sulfur battery, a protective film of the lithium metal anode is used to suppress not only the cycle life of the lithium sulfur battery but also the shuttle phenomenon caused by the reaction between the lithium polysulfide and the lithium metal during charging. Efficient charging was possible and the charging and discharging efficiency and discharge capacity could be increased.

1 is a view schematically showing the structure of a lithium secondary battery according to an embodiment of the present invention.

2 is a graph showing a change in battery voltage according to charge and discharge of a lithium half battery of Comparative Example 1. FIG.

Figure 3 is a graph showing the battery voltage change according to the charge and discharge of the lithium half battery of Example 1 of the present invention.

4 is a graph showing charge and discharge curves of a lithium half battery of Comparative Example 4. FIG.

5 is a graph showing charge and discharge curves of a lithium half battery of Example 10 of the present invention.

Figure 6 is a graph showing the battery capacity and capacity voltage at the 15th cycle by 0.5C discharge and 0.2C charge the battery of Example 11 and Comparative Example 5 of the present invention.

Figure 7 is a graph showing the capacity, voltage and current during the second cycle by 0.2C discharge and 0.2 charge the battery of Example 1 of the present invention.

Claims (38)

An additive capable of forming a polymer film on the surface of the cathode by electrochemical reduction; Non-aqueous organic solvents; And Lithium salt Lithium metal battery electrolyte solution comprising a. The electrolyte of claim 1, wherein the additive has one or more double bonds. The electrolyte of claim 1, wherein the additive has a standard reduction potential in the range of 1.5 to -3.04V. The electrolyte solution for a lithium metal battery according to claim 2, wherein the additive has a standard reduction potential in the range of -1.5 to -3.0V. According to claim 1, wherein the additive is a lithium metal battery electrolyte solution is a substance that forms an anion radical while accepting and reducing electrons when charging the battery on the negative electrode surface. The electrolyte of claim 1, wherein the additive is a substance that forms anionic radicals while being reduced by a chemical reaction. The electrolyte of claim 1, wherein the additive is a substance that provides electrons to the cathode during discharge and forms cationic radicals while being oxidized. The method of claim 1, wherein the additive is a compound having at least one acrylic group; Compounds having at least one allene group; Compounds having at least one allyl group; Compounds having at least one cinnamate group; Compounds having at least one substituted or unsubstituted acryloyl group; A compound having a vinyl group; Compounds having a vinylidene group; Compounds having a styrene group; And a compound having an itaconic group. The method of claim 8, wherein the additive is alkyl acrylate, alkyldiol diacrylate, polyethylene oxide diacrylate, polymethylene oxide diacrylate, polypropylene oxide diacrylate, polytetrafluoroethylene diacrylate, acrylic acid, The electrolyte solution for lithium metal batteries, which is selected from the group consisting of acrylamide and acrylonitrile. The method of claim 8, wherein the additive is alkyl methacrylate, alkyl butyacrylate, alkyldiol dimethacrylate, polyethylene oxide dimethacrylate, polymethylene oxide dimethacrylate, polypropylene oxide dimethacrylate, poly Electrolytic solution for lithium metal batteries, which is selected from the group consisting of tetrafluoroethylene dimethacrylate, methacrylic acid, methacrylamide and methacrylonitrile. The electrolyte solution for a lithium metal battery according to claim 8, wherein the additive is allene or allenyl tributytiltin. The electrolyte of claim 8, wherein the additive is selected from the group consisting of aryl acetate, allyl alcohol, allyl alcohol propoxylate, allylamine, allylaniline, allylanisole, allylbenzene, and allyl bromide. The electrolyte of claim 8, wherein the additive is selected from the group consisting of cinnamic acid, alkyl cinnamate, vinyl cinnamate, cinnamil acetate, cinnamil alcohol, cinnamil bromide, and cinnamil chloride. The electrolyte of claim 8, wherein the additive is acryloyl chloride. The electrolyte of claim 8, wherein the additive is methacryloyl chloride or butacryloyl chloride. The electrolyte of claim 8, wherein the additive is selected from the group consisting of vinyl chloride, trivinyl fluoride, tetravinyl fluoride, vinyl fluoride, trivinyl fluoride and tetravinyl fluoride. The electrolyte of claim 8, wherein the additive is selected from the group consisting of vinylidene fluoride, vinylidene chloride, vinylidene carbonate, vinylidene sulfide, and vinylidene bromide. The electrolyte of claim 8, wherein the additive is selected from the group consisting of styrene, substituted styrene, styrene carboxylic acid, and styrene sulfonic acid. The electrolyte of claim 8, wherein the additive is selected from the group consisting of itaconic acid, itaconyl chloride, and itaconic anhydride. An electrolytic solution containing an additive capable of forming a polymer film on the surface of the cathode by electrochemical reduction, a non-aqueous organic solvent, and a lithium salt; A positive electrode including a positive electrode active material; And Lithium metal or lithium alloy cathode Lithium metal battery comprising a. The lithium metal battery of claim 20, wherein the additive has a standard reduction potential in the range of 1.5 to -3.04V. The lithium metal battery of claim 21, wherein the additive has a standard reduction potential in the range of -1.5 to -3.0V. The lithium metal battery of claim 20, wherein the additive has one or more double bonds. 21. The lithium metal battery of claim 20, wherein the additive is a material that forms anion radicals while accepting and reducing electrons when charging the battery on a negative electrode surface. The lithium metal battery of claim 20, wherein the additive is a substance which forms anionic radicals while being reduced by a chemical reaction. The lithium metal battery of claim 20, wherein the additive is a material that provides electrons to the cathode during discharge and forms cationic radicals while being oxidized. The compound of claim 20, wherein the additive is a compound having at least one acrylic group; Compounds having at least one allene group; Compounds having at least one allyl group; Compounds having at least one cinnamate group; Compounds having at least one substituted or unsubstituted acryloyl group; A compound having a vinyl group; Compounds having a vinylidene group; Compounds having a styrene group; And a compound having an itaconic group. The method of claim 27, wherein the additive is alkyl acrylate, alkyldiol diacrylate, polyethylene oxide diacrylate, polymethylene oxide diacrylate, polypropylene oxide diacrylate, polytetrafluoroethylene diacrylate, acrylic acid, A lithium metal battery selected from the group consisting of acrylamide and acrylonitrile. 28. The method of claim 27 wherein the additive is alkyl methacrylate, alkyl butacrylate, alkyldiol dimethacrylate, polyethylene oxide dimethacrylate, polymethyleneoxide dimethacrylate, polypropylene oxide dimethacrylate, poly A lithium metal battery selected from the group consisting of tetrafluoroethylene dimethacrylate, methacrylic acid, methacrylamide and methacrylonitrile. 28. The lithium metal battery according to claim 27, wherein the additive is allene or allenyl tributinyl tin. 28. The lithium metal battery of claim 27, wherein said additive is selected from the group consisting of aryl acetate, allyl alcohol, allyl alcohol propoxylate, allylamine, allylaniline, allylanisole, allylbenzene, and allyl bromide. 28. The electrolyte of claim 27, wherein the additive is selected from the group consisting of cinnamic acid, alkyl cinnamate, vinyl cinnamate, cinnamil acetate, cinnamil alcohol, cinnamil bromide and cinnamil chloride. The lithium metal battery of claim 27, wherein the additive is acryloyl chloride. The lithium metal battery of claim 27, wherein the additive is methacryloyl chloride or butacryloyl chloride. 28. The lithium metal battery of claim 27, wherein the additive is selected from the group consisting of vinyl chloride, trivinylfluoride, tetravinylfluoride, vinylfluoride, trivinylfluoride and tetravinylfluoride. 28. The lithium metal battery of claim 27, wherein the additive is selected from the group consisting of vinylidene fluoride, vinylidene chloride, vinylidene carbonate, vinylidene sulfide, and vinylidene bromide. The lithium metal battery of claim 27, wherein the additive is selected from the group consisting of styrene, substituted styrene, styrenecarboxylic acid and styrenesulfonic acid. 28. The lithium metal battery of claim 27, wherein the additive is selected from the group consisting of itaconic acid, itaconic chloride and itaconic anhydride.