KR102003306B1 - Lithium electrode and lithium battery compring the same - Google Patents

Abstract

The present invention relates to a lithium electrode and a lithium secondary battery including the lithium electrode, and more particularly, And a lithium ion exchange membrane formed on the lithium metal layer, wherein the lithium ion exchange membrane includes a copolymer of a sulfonamide monomer and a cross-linking monomer to inhibit dendrite growth on the surface of the lithium electrode and improve lithium ion conductivity And excellent performance and life characteristics can be secured.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a lithium secondary battery,

The present invention relates to a lithium electrode including a lithium ion exchange membrane which suppresses the growth of dendrites and exhibits excellent lithium ion conductivity, and a lithium secondary battery comprising the lithium electrode.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is being actively carried out, and some are commercialized.

The lithium secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is laminated or wound, and the electrode assembly is embedded in a battery case, and a non- do. In such a lithium secondary battery, charging and discharging proceed while repeating the process in which lithium ions in the positive electrode are inserted into the negative electrode and desorbed. The capacity of the lithium secondary battery varies depending on the type of the electrode active material, but there is a continuing need for capacity increase and stability improvement.

Therefore, metal-based materials such as silicon (4,200 mAh / g) and tin (990 mAh / g), which exhibit high capacity characteristics and can store and release more lithium ions through the alloying reaction with lithium, are used as an anode active material have. However, when a metal such as silicon or tin is used as a negative electrode active material, the volume expands to about 4 times as much as the lithium alloying process during charging, and shrinks during discharging. The active material is slowly undifferentiated due to a large volume change of the electrode repeatedly generated during charging and discharging, and the capacity is rapidly reduced due to dropping from the electrode, thereby causing difficulties in commercialization.

Compared with the above-mentioned negative electrode active material, lithium metal has a high theoretical energy density of 3,860 mAh / g and a very low standard hydrogen electrode (SHE) of -3.045 V, so a high capacity and high energy density battery can be realized Recently, interest in lithium-sulfur and lithium-air batteries has been increasingly actively studied as an anode active material for lithium secondary batteries.

However, when a lithium metal is used as a cathode of a lithium secondary battery, lithium metal reacts with an electrolyte, an impurity, a lithium salt or the like to form a solid electrolyte interlayer (SEI), and such a passive layer causes a difference in current density Promotes the formation of dendrites in the resin by lithium metal upon charging, and gradually grows upon charging and discharging to cause an internal short circuit between the anode and the cathode. In addition, the dendrite has a mechanically weak portion (bottle neck) to form a dead lithium that loses electrical contact with the current collector during discharge, thereby reducing the capacity of the battery and shortening the cycle life, . Due to the non-uniformity of the redox reaction of the lithium metal anode and the reactivity with the electrolyte, a lithium secondary battery using lithium metal as a cathode has not yet been put to practical use.

In order to solve this problem, various methods such as introducing a polymer protective layer or inorganic solid protective layer on the surface of lithium metal, raising the lithium salt of the electrolyte or introducing suitable additives have been studied.

For example, Korean Patent Laid-Open Publication No. 2016-0034183 discloses a method for forming a protective layer on a negative electrode active layer containing a lithium metal or a lithium alloy, the negative electrode being protected by a polymer matrix capable of accumulating an electrolyte solution to generate electrolyte loss and dendrite formation Can be prevented.

Korean Patent Laid-Open Publication No. 2016-0052351 discloses that the lithium secondary battery can be improved in stability and lifetime characteristics by suppressing the growth of lithium dendrite by including a lithium dendrite absorbent material in the polymer protective film formed on the surface of lithium metal .

These patents stabilize the surface of lithium metal through the protective layer to some extent inhibit the growth of dendrites, but the effect is not sufficient. In addition, when the battery is charged or discharged, the protective layer becomes hard or swells when the battery is contacted with the electrolyte, resulting in denaturation, which limits application to the lithium secondary battery. Therefore, development of a lithium electrode capable of effectively preventing dendrite growth is further required.

Korean Patent Publication No. 2016-0034183 (Mar. 29, 2016), a cathode for a lithium secondary battery and a lithium secondary battery comprising the same Korean Patent Laid-Open Publication No. 2016-0052351 (May 2016), a lithium metal electrode having a stable protective layer and a lithium secondary battery comprising the same

As a result of various studies to solve the above problems, the present inventors have found that by providing a lithium ion exchange membrane containing a sulfonamide monomer and a crosslinkable monomer on a lithium electrode, a local current density difference The dendrite growth was effectively suppressed and the lithium ion conduction specificity was also improved.

Accordingly, an object of the present invention is to provide a lithium electrode and a lithium secondary battery including the lithium electrode, wherein a lithium ion exchange membrane including a sulfonamide monomer and a crosslinkable monomer is formed on a lithium electrode to suppress dendrite growth and improve performance and life will be.

In order to achieve the above object, the present invention provides a lithium secondary battery comprising: a lithium metal layer; And a lithium ion exchange membrane formed on the lithium metal layer, wherein the lithium ion exchange membrane is formed by copolymerizing a sulfonamide monomer represented by the following formula (1) and a crosslinkable monomer:

[Chemical Formula 1]

(In the above formula (1), n, R ₁ , R ₂ and Ar are as described in the description.)

The thickness of the lithium ion exchange membrane is 0.01 to 50 탆.

The crosslinkable monomer may be at least one selected from the group consisting of diethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, dipropylene glycol di Acrylate, dipropylene glycol dimethacrylate, ethylene glycol divinyl ether, ethoxylated trimethylolpropane triacrylate, diethylene glycol divinyl ether, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, Pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, propoxyl (3) Trimethylolpropanetriazole It characterized in that it comprises a relay agent, propoxylate federated (6) trimethylolpropane triacrylate, at least one selected from the group consisting of polyethylene glycol diacrylate and polyethylene glycol dimethacrylate.

Wherein the lithium metal layer comprises lithium metal or a lithium alloy.

In addition, the present invention provides a lithium secondary battery comprising: a lithium metal layer; And a lithium ion exchange membrane formed on the lithium metal layer, wherein the lithium ion exchange membrane comprises a first monomer comprising a functional group capable of binding metal cations and a second monomer comprising a hydrophilic functional group, An amide repeating unit.

Wherein the first monomer is represented by Formula 1 and the second monomer is represented by Formula 2:

 (2)

(In the above formula (2), R ₃ is as described in the specification.)

In addition, the present invention provides a lithium secondary battery including the lithium electrode as a cathode.

The lithium ion exchange membrane according to the present invention can inhibit the growth of lithium dendrites by including the sulfonamide monomer and the crosslinkable monomer and can effectively transfer lithium ions to the lithium metal electrode and has excellent ion conductivity, , Lifetime and stability can be improved.

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

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

As the information and communication industry rapidly develops and the application fields of lithium secondary batteries extend from cell phones and wireless electronic devices to electric vehicles, lithium secondary batteries, which are capable of miniaturization, light weight, thinness, and portability and have high performance and high stability, Has been demanded.

In response to this demand, a lithium metal battery (LMB) using lithium metal as a cathode has recently been spotlighted. Lithium metal is expected to be a cathode material for high capacity lithium secondary batteries because it has high energy density (3,860 mAh / g) while lowering oxidation / reduction potential (-3.045 V vs standard hydrogen electrode) and atomic weight (6.94 g / a.u.).

However, when a lithium metal is used as a cathode, a passive layer is formed by reacting with an organic solvent, a lithium salt, impurities present in the battery, etc. forming the electrolyte, and the passive layer causes a local current density difference to form a dendritic lithium dendrite . The lithium dendrite not only shortens the lifetime of the lithium secondary battery but also causes short-circuit in the battery and inert lithium to increase the physical and chemical instability of the lithium secondary battery and adversely affect the charge and discharge capacity. In addition, the passive layer is thermally unstable, so that the charging and discharging of the battery can be continuously progressed, or gradually collapsed due to increased electrochemical energy and thermal energy, especially at high temperature storage in a fully charged state. As a result of such collapse of the passivation layer, a side reaction in which the exposed lithium metal surface is directly reacted with the electrolyte solvent to decompose is continuously generated, thereby increasing the resistance of the negative electrode and reducing the charge / discharge efficiency of the battery. In addition, when the passivation layer is formed, the solvent of the electrolyte is consumed, and the lifetime of the battery is reduced due to by-products, gas, and the like generated during various side reactions such as formation and collapse of the passivation layer and decomposition of the electrolyte.

For this purpose, in the prior art, the composition of the electrolyte is changed or a separate protective layer is introduced on the surface of the lithium metal, but the stability of the lithium metal electrode is not effectively improved.

In the present invention, in order to suppress the dendrite growth on the surface of the lithium electrode and to secure the effect of improving the performance and lifetime of the lithium secondary battery, a lithium ion exchange membrane comprising a monomer containing a sulfonamide repeating unit and a cross- (Li) ion exchange membrane (LEM).

A lithium electrode according to an embodiment of the present invention includes a lithium metal layer; And a lithium ion exchange membrane formed on the lithium metal layer, wherein the lithium ion exchange membrane comprises a copolymer of a sulfonamide monomer represented by the following formula (1) and a crosslinkable monomer.

The lithium metal layer is an anode active material capable of reversibly intercalating and deintercalating lithium ions, and may include a lithium metal or a lithium alloy.

The lithium alloy may be, for example, an alloy of lithium and a metal of Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga or Cd.

The lithium metal layer may be in the form of a foil or a metal powder.

The thickness of the lithium metal layer is not particularly limited, but may be, for example, 5 to 200 탆, and preferably 10 to 100 탆. When the thickness of the lithium metal layer 20 falls within the above range, ions and electrons in the cathode can be smoothly transferred.

The lithium metal layer may optionally further comprise a current collector.

The current collector is for supporting the above-described lithium metal layer and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of the lithium secondary battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, palladium, sintered carbon, surface treated with carbon, nickel, silver or the like on a surface of copper or stainless steel, .

The current collector may have fine irregularities on the surface thereof to enhance the bonding force with the lithium metal layer, and various forms such as a film, a sheet, a foil, a mesh, a net, a porous body, a foam, and a nonwoven fabric may be used.

The thickness of the current collector is not particularly limited and may be suitably determined according to the application. For example, the current collector may have a thickness of 3 to 500 mu m, preferably 5 to 100 mu m, and more preferably 5 to 50 mu m. If the thickness of the current collector is less than the above range, the durability is lowered. On the contrary, if the thickness exceeds the above range, the capacity per unit volume of the lithium secondary battery may decrease.

The binder acts as a paste for the anode active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, buffering effect on expansion and contraction of the active material, and the like. Specifically, the binder is selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer including ethylene oxide, polyvinyl pyrrolidone, polyurethane , Polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

The method of forming the lithium metal layer is not particularly limited, and a layer or a film forming method commonly used in the art can be used. For example, a method such as compression, coating, or deposition may be used. In addition, the present invention includes a case where a metal lithium thin film is formed on a metal plate by initial charging after assembling the battery without a lithium thin film in the current collector. In addition, the width of the negative electrode active material layer or the lithium metal plate may be adjusted according to the shape of the electrode to facilitate the production of the electrode.

 The lithium ion exchange membrane is formed on the lithium metal layer and selectively passes only lithium ions. Therefore, the lithium ion exchange membrane has excellent lithium ion conductivity, thereby minimizing the concentration gradient between the lithium ions on the lithium metal surface and inducing the uniformity of the current density, thereby suppressing the growth of the dendrite. In addition, the lithium ion exchange membrane protects the lithium metal layer so as to exhibit improved durability.

The lithium ion exchange membrane may be a copolymer formed by a polymerization reaction between a sulfonamide monomer represented by the following formula (1) and a crosslinkable monomer:

[Chemical Formula 1]

(In the formula 1,

n is an integer from 2 to 10;

R ₁ is a halogen group, a haloalkyl _{group, -CN, -COOR 2, -C (} = O) R 2, -CON (R 2) 2, -CONR 2 H, -SO 3 R 2, -SO (OR 2) _{2, -SO (oR 2) H} , -SOR 2, -SO 2 R 2, -Ar-SO 3 R 2, -PO (oR 2) 2, -PO (oR 2) H, -NO 2 or -OR ₂ ;

R ₂ is independently hydrogen, a halogen group, a metal cation or an aliphatic hydrocarbon group having 1 to 20 carbon atoms;

Ar is an arylene group or a heteroarylene group.)

The term " halogen " as used herein is fluorine (F), chlorine (Cl), bromine (Br) or iodine (I) unless otherwise stated.

The term " haloalkyl group " as used in the present invention means an alkyl group substituted with halogen unless otherwise stated.

As used herein, the term " aliphatic hydrocarbon group " refers to a group that does not contain an aromatic ring and has a carbon skeleton relative to the aromatic group, wherein the carbon in the carbon skeleton includes oxygen (O), nitrogen (N) S) may be substituted for at least one of them. The aliphatic hydrocarbon group may include straight chain, branched chain, monocyclic or polycyclic ring. Examples of the aliphatic hydrocarbon group include a linear or branched alkyl group having 1 to 20 carbon atoms, a linear or branched alkoxy group having 2 to 20 carbon atoms, a straight or branched alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, But are not limited to, a cycloalkyl group having 3 to 20 carbon atoms, a cycloalkenyl group having 3 to 20 carbon atoms, a cycloalkynyl group having 3 to 20 carbon atoms, and the like.

The term " alkyl group " used in the present invention may be linear or branched, and the number of carbon atoms is not particularly limited, but is preferably 1 to 20, Specific examples include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, t-butyl, pentyl, hexyl and heptyl.

The term " alkoxy group " used in the present invention means an alkyl group having 1 to 20 carbon atoms having an oxygen atom through an ether bond at the carbon chain terminal unless otherwise specified, but is not limited thereto.

The term " alkenyl group " as used in the present invention means a hydrocarbon group having 1 to 20 carbon atoms including at least one carbon-carbon double bond unless otherwise stated, but is not limited thereto. The alkenyl group may be optionally substituted with one or more substituents.

The term " alkynyl group " used in the present invention means, unless otherwise stated, a hydrocarbon group of 1 to 20 carbon atoms containing at least one carbon-carbon triple bond, but is not limited thereto. The alkynyl group may be optionally substituted with one or more substituents.

The term " cycloalkyl group " as used herein refers to a non-aromatic carbon-based ring consisting of at least three carbon atoms. Such cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and the like, but are not limited thereto.

The term " cycloalkenyl group " as used in the present invention means a non-aromatic carbon-based ring having at least one carbon-carbon double bond and having a designated carbon number.

As used herein, the term " cycloalkynyl " means a non-aromatic carbocyclic ring having at least one carbon-carbon triple bond and having a designated carbon number.

The term " arylene group " used in the present invention means a divalent aromatic carbon-based ring and the number of carbon atoms may be 6 to 60, specifically 6 to 40, more specifically 6 to 25. The arylene group may include a structure in which two or more rings are condensed or bonded, and the other ring may be aromatic, non-aromatic, or a combination thereof. For example, the arylene group may be selected from the group consisting of phenylene, biphenylene, naphthylene, anthracenylene, phenanthrenylene, triphenylrenylene, chryshenylene, benzochrycyanylene, fluorenylene, spirobiflourenylene But are not limited to these.

The term " heteroarylene group " as used herein means an arylene group in which at least one carbon is replaced by a heteroatom. The heteroatom means nitrogen (N), oxygen (O), sulfur (S), phosphorus (P) and silicon (Si). For example, the heteroarylene group may be at least one selected from the group consisting of pyridylene, imidazopyridylene, pyrimidylene, triazienylene, carbazolylene, benzimidazolylene, benzocarbazolylene, dibenzocarbazolylene, quinolinylene, iso And examples thereof include quinolinylene, quinolinylene, quinazolinylene, pyrazoloquinazolinylene, imidazoquinazolinylene, thiazolylene, benzothiazolylene, phenanthrolinylene, phenanthridinylene, dibenzoacridinylene, , Dibenzoylolylene, spirobidibenzoylsilylene, and the like, but are not limited thereto.

The metal cation may be an alkali metal ion, preferably a lithium ion.

The sulfonamide monomer may include a sulfonamide structure including a lithium ion conductive moiety having a fixed anion, thereby transferring lithium ions. In addition, by repeatedly incorporating the sulfonamide structure that allows only lithium ions to migrate, it is possible to exhibit more improved lithium ion conduction characteristics than conventional single ion conducting materials.

The sulfonamide monomer represented by the formula (1) may be represented by the following formulas (1-1), (1-2) and (1-3)

[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

In the above formulas 1-1 to 1-3, n is an integer of 2 to 10, preferably an integer of 2 to 5.

The crosslinkable monomer has a role of connecting or crosslinking the polymer chains composed of the above-mentioned sulfonamide-based monomer. By the crosslinking monomer, the lithium ion exchange membrane according to the present invention can form a three-dimensional crosslinked network structure and thus can easily transfer lithium ions through the entanglement of the polymer chains. Specifically, the lithium ion exchange membrane according to the present invention has a cross-linked structure in the form of a net through the crosslinkable monomer, so that the lithium ion exchange membrane composed of the conventional linear polymer has a functional group capable of being lithiated per unit area, The lithium ion conductivity can be improved. In addition, the three-dimensional network structure through the crosslinkable monomer can impart durability and electrolyte stability to the lithium ion exchange membrane by imparting stronger physical properties thereto.

The crosslinkable monomer may be a polyfunctional acrylate monomer and is not particularly limited as long as it is a compound having two or more double bonds at the terminals.

For example, the crosslinking monomer may be selected from the group consisting of diethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate (1, 6-hexanediol diacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, dipropylene diacrylate, dipropylene glycol dimethacrylate ( dipropylene glycol dimethacrylate, ethylene glycol divinyl ether, ethoxylated (6) trimethylolpropane triacrylate, diethylene glycol divinyl ether (6) trimethylolpropane triacrylate, Triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, but are not limited to, polyacrylic acid, polyacrylic acid, polyacrylic acid, polyacrylic acid, polyacrylic acid, polyacrylic acid, polyacrylic acid, polyacrylic acid, polyacrylic acid, polyacrylic acid, polyacrylic acid, polyacrylic acid, dipentaerythritol hexaacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, propoxylated (3) trimethylolpropane triacrylate, and propoxylated trimethylolpropane triacrylate. Propoxylated (6) trimethylopropane triacrylate, poly (ethylene glycol) diacrylate, and poly (ethylene glycol) dimethacrylate (6) trimethylolpropane triacrylate. Done Since it may include at least one selected.

In this case, the weight ratio of the sulfonamide monomer to the crosslinkable monomer may be 99: 1 to 1:99, and preferably 75:25 to 25:75. When the weight ratio falls within the above range, a lithium ion exchange membrane can be stably formed, and the formed film can exhibit excellent lithium ion conduction characteristics and mechanical strength.

In the lithium electrode according to one embodiment of the present invention, the lithium ion exchange membrane includes a copolymer formed through a polymerization reaction of the sulfonamide monomer and the crosslinkable monomer. The polymerization reaction may be carried out by mixing the sulfonamide monomer and the crosslinkable monomer in a solvent and then adding a photoinitiator.

The solvent can be used without limitation as long as it is commonly used in a lithium secondary battery, except that the solvent is highly reactive with lithium such as water, alcohol, and acetonitrile.

The photoinitiator is not particularly limited as long as it can be used in a photopolymerization reaction. For example, the photoinitiator may be selected from the group consisting of 1-phenyl-2-hydroxy-2-methyl propane-1-one, chloroacetophenone, But are not limited to, diethoxyacetophenone, hydroxyacetophenone, 1-hydroxycyclohexyl phenyl ketone,? -Amino acetophenone, benzoin ether Benzyl Dimethyl Ketal, BenzoPhenone, Thioxanthone, and the like, but are not limited thereto.

The photopolymerization of the sulfonamide-based monomer and the crosslinkable monomer to form the crosslinked polymer can be performed by irradiating ultraviolet (UV) light to the mixture of the above-mentioned composition. In this case, polymerization can be carried out very quickly.

The copolymer may be an alternating copolymer, a block copolymer, a random copolymer or a graft copolymer.

The weight average molecular weight of the copolymer is preferably 10,000 to 1,000,000 g / mol, more preferably 50,000 to 500,000 g / mol, and still more preferably 50,000 to 200,000 g / mol. When the weight average molecular weight of the copolymer falls within the above range, sufficient mechanical properties and lithium ion conductivity as a lithium ion exchange membrane can be secured.

The lithium ion exchange membrane can be formed by a coating film forming method commonly used in the art. Wet coating methods such as gravure coating, slot die coating, spin coating, spray coating, bar coating, and dip coating; A dry coating method such as thermal evaporation, E-beam evaporation, chemical vapor deposition (CVD), or sputtering may be used.

The thickness of the lithium ion exchange membrane may be 0.01 to 50 탆, preferably 0.1 to 20 탆. If the thickness of the lithium ion exchange membrane is less than the above range, the durability of the lithium ion exchange membrane is lowered. On the other hand, if the thickness exceeds the above range, resistance may be applied to decrease the electrical performance of the electrode or increase the volume of the electrode.

According to another aspect of the present invention, there is provided a lithium electrode comprising: a lithium metal layer; And a lithium ion exchange membrane formed on the lithium metal layer, wherein the lithium ion exchange membrane comprises a first monomer including a functional group capable of binding metal cations and a second monomer including a hydrophilic functional group, Amide repeat units.

The lithium metal layer is as described in one embodiment of the present invention.

The first monomer includes a functional group capable of binding with a metal cation, and may be represented by the following Formula 1:

 [Chemical Formula 1]

In Formula 1, n, R ₁ , R _2, and Ar are as described in the embodiment of the present invention.

The second monomer comprises a hydrophilic functional group and may be represented by the following general formula (2)

(2)

(In the formula (2)

R ₃ is an aromatic hydrocarbon group having 6 to 20 carbon atoms and containing a functional group selected from the group consisting of an ether group, an ester group, a carbonate group, a carboxylic acid group, an aldehyde group, a ketone group and a hydroxyl group.

As used herein, the term "ether" is represented by the formula AOA ¹ , wherein A and A ¹ are independently selected from the group consisting of alkyl, haloalkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, Heterocycloalkyl or heterocycloalkenyl group.

As used herein, the term " ester " is represented by the formula -C (O) OA where A is an alkyl, haloalkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, Heterocycloalkyl or heterocycloalkenyl group.

The term "carbonate" as used herein is represented by the formula -OC (O) OR, wherein R is hydrogen, alkyl, alkenyl, alkynyl, aryl, cycloalkyl, haloalkyl or heterocycloalkyl group as described above.

The term " carboxylic acid ", as used herein, is represented by the formula -C (O) OH.

The term " aldehyde ", as used herein, is represented by the formula -C (O) H.

As used herein, the term "ketone" is represented by -C (O) R, where R is alkyl, alkenyl, alkynyl, aryl, cycloalkyl, haloalkyl or heterocycloalkyl group as described above.

The term " hydroxy ", as used herein, is represented by the formula -OH.

As used herein, the term " aromatic hydrocarbon group " means a group having at least one valence and containing at least one aromatic group and having a carbon skeleton, wherein the carbon in the carbon skeleton is oxygen (O), nitrogen (N) ) May be substituted with at least one selected from the group consisting of The aromatic hydrocarbon group may be an aryl group having 6 to 60 carbon atoms or an arylene group.

The weight ratio of the first monomer to the second monomer may be from 99: 1 to 1:99, and preferably from 75:25 to 25:75. When the weight ratio falls within the above range, a lithium ion exchange membrane can be stably formed, and the formed film can exhibit excellent lithium ion conduction characteristics and mechanical strength.

In the lithium electrode according to another embodiment of the present invention, the lithium ion exchange membrane includes a copolymer formed through a polymerization reaction of the first monomer and the second monomer. At this time, the above-mentioned crosslinkable monomer may be further included.

The method and thickness of the lithium ion exchange membrane including the above polymerization reaction are as described in the embodiment of the present invention described above.

The lithium ion exchange membrane described above may have a lithium ion conductivity (sigma) of 1.0 x 10 ^-7 to 5 x 10 ^-4 S / cm and a lithium ion transfer number of 0.4 to 1.0. In particular, the lithium ion exchange membrane according to the present invention can exhibit improved lithium ion conduction characteristics by forming a three-dimensional crosslinked network structure by copolymerizing a sulfonamide structure capable of transferring lithium ions with a monomer containing a repeating unit together with a crosslinkable monomer have. In addition, the lithium ion exchange membrane has basically an electrolyte uptake of a certain level and can exhibit improved durability and electrolyte stability through the crosslinked structure described above.

The present invention also provides a lithium secondary battery including the lithium electrode as a cathode.

The lithium secondary battery includes a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode, and the negative electrode may include a lithium electrode including the lithium ion exchange membrane.

The positive electrode may be formed into a positive electrode by forming a composition including a positive electrode active material, a conductive material and a binder on a positive electrode current collector.

The positive electrode active material is _{LiCoO 2, LiNiO 2, LiMnO 2} , LiMn 2 O 4, Li (Ni a Co b Mn c) O 2 (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi 1 - y CoyO 2, LiCo 1 - y MnyO 2, LiNi 1 - y MnyO 2 (O≤y <1), Li (Ni a Co b Mn c) O 4 (0 <a <2, 0 <b <2 , 0 <c <2, a + b + c = 2), LiMn 2 - z NizO 4, LiMn 2 - z CozO 4 (0 <z <2), LiCoPO 4 and LiFePO ₄ , Or a mixture of two or more of them may be used. In addition to these oxides, sulfide, selenide and halide may be used.

The conductive material is a component for further improving the conductivity of the cathode active material, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder has a function of holding the positive electrode active material on the positive electrode collector and organically connecting the positive electrode active materials. Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethylcellulose CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene- Rubber, various copolymers thereof, and the like.

The positive electrode current collector is as described above in the current collector, and an aluminum thin plate may be generally used for the positive electrode current collector.

The positive electrode composition may be coated on the positive electrode current collector by a conventional method known in the art. For example, a dipping method, a spray method, a roll court method, a gravure printing method A bar coating method, a die coating method, a comma coating method, or a mixing method thereof may be used.

The anode and cathode compositions thus coated are then subjected to a drying process to evaporate the solvent or dispersion medium, to ensure the denseness of the coating film, and to the adhesion between the coating film and the current collector. The drying is carried out according to a conventional method, and is not particularly limited.

The electrolyte may be a non-aqueous electrolyte or a solid electrolyte which does not react with lithium metal, but is preferably a nonaqueous electrolyte, and includes an electrolyte salt and an organic solvent.

The electrolyte salt contained in the non-aqueous electrolyte is a lithium salt. The lithium salt can be used without limitation as long as it is commonly used in an electrolyte for a lithium secondary battery. For example, 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 , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, and imide may be used.

Examples of the organic solvent included in the non-aqueous electrolyte include those commonly used in an electrolyte for a lithium secondary battery, such as an ether, an ester, an amide, a linear carbonate, and a cyclic carbonate, Can be used. Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a mixture thereof may be included.

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, Propylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

Specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate And mixtures of two or more of them may be used as typical examples, but the present invention is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, are highly viscous organic solvents having a high permittivity and can dissociate the lithium salt in the electrolyte more easily. Such cyclic carbonates may be used in the form of dimethyl carbonate and diethyl carbonate When a low viscosity, low dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having a higher electric conductivity can be produced.

As the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used , But is not limited thereto.

Examples of the ester in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.

The injection of the nonaqueous electrolyte solution can be performed at an appropriate stage of the manufacturing process of the electrochemical device according to the manufacturing process and required properties of the final product. That is, it can be applied before assembling the electrochemical device or in the final stage of assembling the electrochemical device.

The separator may be additionally provided between the anode and the cathode. The separator separates or insulates the positive electrode and the negative electrode from each other and enables lithium ion transport between the positive electrode and the negative electrode, and may be made of a porous nonconductive or insulating material. Such a separation membrane may be an independent member such as a film, or may be a coating layer added to the anode and / or the cathode.

The separation membrane is not particularly limited in its material and can be used without any particular limitation as long as it separates the anode and the cathode physically and has an electrolyte and an ion permeability and can be used as a separation membrane in an electrochemical device. It is preferable that the material is a conductive or insulating material, particularly a material having low resistance against ion movement of the electrolytic solution and excellent ability to impregnate the electrolytic solution. For example, a polyolefin-based porous membrane or nonwoven fabric may be used, but it is not particularly limited thereto.

Examples of the polyolefin-based porous film include polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, and polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene and ultra high molecular weight polyethylene, One can say.

The nonwoven fabric may contain, in addition to the polyolefin-based nonwoven fabric, a polyphenylene oxide, a polyimide, a polyamide, a polycarbonate, a polyethyleneterephthalate, a polyethylene naphthalate, Polybutyleneterephthalate, polyphenylenesulfide, polyacetal, polyethersulfone, polyetheretherketone, polyester, and the like may be used alone or in combination of two or more. The nonwoven fabric may be a spunbond or a meltblown fiber composed of long fibers. The nonwoven fabric may be a porous web.

The thickness of the separation membrane is not particularly limited, but is preferably in the range of 1 to 100 mu m, more preferably in the range of 5 to 50 mu m. If the thickness of the separator is less than 1 탆, the mechanical properties can not be maintained. If the thickness exceeds 100 탆, the separator will act as a resistive layer and the performance of the battery will be deteriorated.

The pore size and porosity of the separation membrane are not particularly limited, but it is preferable that the pore size is 0.1 to 50 탆 and the porosity is 10 to 95%. If the pore size of the separator is less than 0.1 μm or the porosity is less than 10%, the separator will act as a resistive layer. If the pore size exceeds 50 μm or the porosity exceeds 95%, mechanical properties can not be maintained .

The lithium secondary battery according to the present invention can be laminated, stacked, and folded in addition to winding, which is a general process.

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

Also, the present invention provides a battery module including the lithium secondary battery as a unit cell, and provides the battery pack including the battery module.

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

Examples of the above medium and large-sized devices include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); An electric motorcycle including an electric bike (E-bike) and an electric scooter (Escooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

Example  And Comparative Example

[Example 1]

A solution of the monomer of Formula 1-1 and the dipentaerythritol pentaacrylate in the weight ratio of 95: 5, in which n = 5, was directly coated on a lithium foil having a thickness of 20 탆 with a doctor blade and dried at room temperature to prepare a 5 탆 thick To form a lithium ion exchange membrane. At this time

[Example 2]

A lithium electrode was prepared in the same manner as in Example 1, except that the monomer of Formula 1-3 was used in place of the monomer of Formula 1-1 in Example 1.

[Comparative Example 1]

A lithium electrode was prepared in the same manner as in Example 1 except that a lithium ion exchange membrane was not formed.

[Comparative Example 2]

A lithium electrode was prepared in the same manner as in Example 1 except that a lithium ion exchange membrane was formed as a solution in which polyethylene oxide containing lithium bisfluorosulfonyl imide (LiFSI) was dispersed.

Experimental Example  One. Lithium ion  Conductivity (σ) measurement

The ion conductivity of the lithium electrode prepared in Examples 1 and 2 and Comparative Example 2 was measured at 25 ° C from the response obtained by applying AC with two shield electrodes using an impedance analyzer (Zahner, IM6). The results obtained are shown in Table 1 below.

Experimental Example  2. Li / Li Of the symmetric cell  Performance evaluation

The lithium electrode prepared in the above Examples and Comparative Examples was used as a negative electrode. The electrolytic solution was prepared by dissolving 1 M lithium bisfluorosulfonyl imide (LiFSI) in an organic solvent composed of 1,3-dioxolane and ethylene glycol dimethyl ether (DOL: DME = 1: 1 (volume ratio)).

A Li / Li symmetric cell was prepared from the negative electrode and the electrolyte.

The performance of the fabricated Li / Li symmetric cell was measured by the following method.

(1) Lithium ion transference number

The lithium ion transition number was measured by a constant voltage polarization curve method. The initial and steady state values of the cell currents before and after polarization in the Faraday cage were measured at a small polarization voltage of 10 mV using a potentiostat (BioRodirect, VSP). The initial and steady-state values of the contact resistance before and after the constant-voltage polarization curve were measured by resistance measurement (10 mHz to 200 kHz). The results obtained are shown in Table 1 below.

(2) Cycle efficiency

The symmetric cells were charged and discharged under conditions of 83% depth of discharge (DOD) and 1 C charge / discharge conditions. After the charge / discharge, the cycle efficiency (%) was measured. The results obtained are shown in Table 1 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Lithium ion conductivity
(?, S / cm) 4X10 ^-5 to 5X10 ^-5 4X10 ^-5 to 5X10 ^-5 - 3X10 ^-6 Lithium ion transition number 0.85 0.9 0.45 0.5 Cycle efficiency (%) 99.5 99.6 99.35 99.4

Referring to Table 1, it was confirmed that the lithium ion conductivity, lithium ion transfer number and cycle efficiency of the lithium electrodes of Examples 1 and 2 according to the present invention were generally good and their values were improved compared with Comparative Examples .

The lithium electrode according to the present invention has a lithium ion exchange membrane including a sulfonamide monomer and a crosslinkable monomer on a lithium metal layer, thereby preventing the lithium dendrite from growing and improving lithium ion conduction characteristics, High capacity, high stability, and long life.

Claims (8)

A lithium metal layer; And
And a lithium ion exchange membrane formed on the lithium metal layer,
Wherein the lithium ion exchange membrane comprises a copolymer of a sulfonamide monomer represented by the following formula (1) and a crosslinkable monomer:
[Chemical Formula 1]

(In the formula 1,
n is an integer from 2 to 10;
R ₁ is a halogen group, a haloalkyl _{group, -CN, -COOR 2, -C (} = O) R 2, -CON (R 2) 2, -CONR 2 H, -SO 3 R 2, -SO (OR 2) _{2, -SO (oR 2) H} , -SOR 2, -SO 2 R 2, -Ar-SO 3 R 2, -PO (oR 2) 2, -PO (oR 2) H, -NO 2 or -OR ₂ ;
R ₂ is independently hydrogen, a halogen group, a metal cation or an aliphatic hydrocarbon group having 1 to 20 carbon atoms;
Ar is an arylene group or a heteroarylene group.) The method according to claim 1,
Wherein the lithium ion exchange membrane has a thickness of 0.01 to 50 占 퐉. The method according to claim 1,
The crosslinkable monomer may be selected from the group consisting of diethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, diethylene glycol dimethacrylate, ethylene glycol di Methacrylate, dipropylene glycol diacrylate, dipropylene glycol dimethacrylate, ethylene glycol divinyl ether, ethoxylated trimethylolpropane triacrylate, diethylene glycol divinyl ether, triethylene glycol dimethacrylate , Tetraethylene glycol diacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, trimethylol propane triacrylate, trimethylol Propane triacrylate, propane triacrylate, propane triacrylate, propane triacrylate, (6) trimethylolpropane triacrylate, polyethylene glycol diacrylate, and polyethylene glycol dimethacrylate. 7. The lithium electrode according to claim 1, wherein the lithium ion conductive polymer is at least one selected from the group consisting of ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate and polyethylene glycol dimethacrylate. The method according to claim 1,
Wherein the lithium metal layer comprises lithium metal or a lithium alloy. A lithium metal layer; And
And a lithium ion exchange membrane formed on the lithium metal layer,
Wherein the lithium ion exchange membrane comprises a first monomer comprising a functional group capable of binding metal cations and a second monomer comprising a hydrophilic functional group,
Wherein the first monomer comprises a sulfonamide repeating unit. 6. The method of claim 5,
Wherein the first monomer is represented by the following Formula 1:
[Chemical Formula 1]

(In the formula 1,
n is an integer from 2 to 10;
R ₁ is a halogen group, a haloalkyl _{group, -CN, -COOR 2, -C (} = O) R 2, -CON (R 2) 2, -CONR 2 H, -SO 3 R 2, -SO (OR 2) _{2, -SO (oR 2) H} , -SOR 2, -SO 2 R 2, -Ar-SO 3 R 2, -PO (oR 2) 2, -PO (oR 2) H, -NO 2 or -OR ₂ ;
R ₂ is independently hydrogen, a halogen group, a metal cation or an aliphatic hydrocarbon group having 1 to 20 carbon atoms;
Ar is an arylene group or a heteroarylene group.) 6. The method of claim 5,
Wherein the second monomer is represented by the following Formula 2:
(2)

(In the formula (2)
R ₃ is an aromatic hydrocarbon group having 6 to 20 carbon atoms and containing a functional group selected from the group consisting of an ether group, an ester group, a carbonate group, a carboxylic acid group, an aldehyde group, a ketone group and a hydroxyl group. 1. A lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode,
Wherein the cathode is the lithium electrode according to any one of claims 1 to 5.