KR20050030762A - Negative electrode for rechargeable lithium battery, method of producing same, and rechargeable lithium battery comprising same - Google Patents

Abstract

Provided are a negative electrode for a lithium battery where a barrier layer are uniformly in physical contact with a lithium metal to allow the reaction at a negative electrode be occurred uniformly, its preparation method, and a lithium battery containing the negative electrode which is improved in lifetime characteristics and capacity characteristics. The negative electrode(12) comprises a lithium metal; and a barrier layer(13) comprising an inorganic material and a polymer in a ratio of 50-90 : 50-10 by weight formed on the lithium metal. Preferably the inorganic material is selected from the group consisting of silica, alumina, titanium oxide, zeolite, silicate and barium titanium oxide; and the polymer is selected from the group consisting of a polyvinylidene fluoride-based polymer, a polytetrafluoroethylene-based polymer, a poly(vinyl chloride)-based polymer, a poly(vinyl alcohol)-based polymer, a polyimide-based polymer and a polyethylene oxide-based polymer.

Description

A negative electrode for a lithium battery, a method of manufacturing the same, and a lithium battery including the same TECHNICAL FIELD

[Industrial use]

The present invention relates to a negative electrode for a lithium battery, a method for manufacturing the same, and a lithium battery including the same, and more particularly, to a negative electrode for a lithium battery, a method for manufacturing the same, and a lithium battery including the same having excellent electrolyte solution impregnation and no battery short circuit problem. .

[Prior art]

Recently, with the development of the high-tech electronic industry, it is possible to reduce the weight and weight of electronic equipment, thereby increasing the use of portable electronic devices. As a power source for such portable electronic devices, the need for a battery having a high energy density has increased, and research on lithium batteries has been actively conducted.

Among these lithium batteries, lithium sulfur batteries have a much higher theoretical energy density of 2800 Wh / kg (1675 mAh / g) than other battery systems. Sulfur is also attracting attention as an inexpensive, environmentally friendly material with abundant resources. Therefore, many researchers are working on the construction of lithium batteries using sulfur.

Lithium metal is widely used as a negative electrode active material in lithium sulfur batteries because of its light weight and excellent energy density. However, since lithium metal has an electrochemical reaction on the surface of the lithium metal, physical contact between the separator and the lithium metal should occur uniformly. However, the porous polyethylene separator used as a conventional separator has a problem that it is difficult to form a uniform physical contact with the lithium metal anode.

In order to solve this problem, Korean Patent Laid-Open Publication No. 2001-92193 discloses a method of manufacturing an electrode in which an electrode and a porous separator are integrated by coating an electrolyte-compatible polymer on at least one of a cathode and an anode. In addition, 2001-95643 describes the integration of an electrode with a polymer electrolyte.

However, this method has to be carried out a process of coating the polymer film on the electrode, there is a problem that the uniform contact between the separator and the cathode is not sufficient.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a negative electrode for a lithium battery integrated so that the lithium metal and the separator can be uniformly contacted.

Another object of the present invention is to provide a method for producing a negative electrode for a lithium battery, which can produce the negative electrode in a simple process.

Still another object of the present invention is to provide a lithium battery having improved life characteristics including the negative electrode.

In order to achieve the above object, the present invention is lithium metal; And it provides a negative electrode for a lithium battery comprising an isolation layer comprising an inorganic material and a polymer formed in the lithium metal in a 50 to 90: 50 to 10 weight ratio.

The present invention also provides a method for producing a negative electrode for a lithium battery comprising the step of coating a lithium metal with an insulating layer comprising an inorganic material and a polymer.

The present invention also provides a lithium battery including the cathode and an electrolyte including the cathode, a cathode active material capable of occluding and detaching lithium ions.

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

The present invention relates to a negative electrode for a lithium battery in which a separator is coated on lithium metal so that the lithium metal negative electrode and the separator are in uniform physical contact with each other.

That is, the negative electrode of this invention contains lithium metal and the isolation layer formed in this lithium metal. The isolation layer includes an inorganic material and a polymer in a weight ratio of 50 to 90:50 to 10. The inorganic material may increase punctual strength to prevent battery short-circuits even when the insulating layer is thinly formed to a thickness of 10 micrometers or less. As the inorganic material, one or more selected from the group consisting of silica, alumina, titanium oxide, zeolite, silicate, and barium titanium oxide may be used.

As the polymer, all the polymers used in the manufacture of a separator in a conventional lithium battery may be used, and representative examples thereof include polyvinylidene-based polymer, polytetrafluoroethylene-based polymer, polyvinylchloride-based polymer, polyvinyl alcohol-based polymer, and poly A mid series polymer or a polyethylene oxide series polymer may be used. As the polyvinylidene-based polymer, polyvinylidene chloride, polyvinylidene fluoride, and the like may be used, and as the polytetrafluoroethylene-based polymer, polytetrafluoroethylene, nafion, plemion, and the like may be used. . The polyvinyl chloride-based polymer may be polyvinyl chloride, polyvinyl chloride-vinylacetate copolymer, and the like, and the polyvinyl alcohol-based polymer may be polyvinyl alcohol, polyvinyl alcohol-vinylacetate copolymer, or the like. It can be used. The polyimide series includes all polyimides produced from diamines and dicarboxylic acids, and includes polyimide chains other than polyimides, such as polyether imides, polyamide imides, and polycarbonate imides. There may be. Examples of the polyimide series include Kevlar and Ultem. The polyethylene oxide-based polymer may be polyethylene oxide, polyethylene oxide-propylene oxide copolymer, polyethylene diacrylate, polyethylene dimethacrylate and the like.

When the amount of the inorganic material is reduced in the ratio of the inorganic material and the polymer, there is a problem that the ion conductivity of the insulating layer is reduced, and when the amount of the inorganic material is increased, the impact strength of the insulating layer is low, so that the crack or crack easily occurs. There is this.

The isolation layer is a porous layer having a porosity of 20 to 70%. Due to this porosity, the electrolyte content is high, so that the ion conductivity may be improved.

The isolation layer is integrated with the isolation layer and lithium metal to ensure uniformity of the reaction at the negative electrode, thereby suppressing the concentration of the negative electrode reaction, thereby improving cycle life characteristics of the battery. In addition, in general, the inorganic separator is excellent in breaking strength, but the tensile strength (tensile strength) is difficult to wind the winding process, but the negative electrode of the present invention can solve the manufacturing problems due to the low tensile strength of the separator coated with lithium metal have.

In the cathode of the present invention, the isolation layer may be formed by a coating process, or may be laminated with a separator film. In the laminating method, the separator film and the lithium metal may be laminated, and after the release film is coated on the separator, the release film is not coated and the release film may be removed after laminating the lithium metal.

Among them, since the coating process is the simplest and preferred, the coating process will be described in more detail.

The inorganic material and the polymer in a lithium metal in a weight ratio of 50 to 95: 50 to 10 and liquid-coated the separation layer composition containing a solvent, and then the solvent is volatilized to form a separation layer on the lithium metal . At this time, pores are formed in the isolation layer when the solvent is volatilized to form a porous isolation layer. In the isolation layer composition, a solvent having high volatility and low reactivity with a lithium negative electrode may be used, and representative examples thereof may be ether, ester, amide, and alcohol. For example, tetrahydrofuran, dioxolane, ethyl methyl ether, diethyl ether, acetone, N-methylpyrrolidone, dimethyl sulfoxide, dimethyl acetate, ethanol, methanol, isopropyl alcohol, and the like are possible.

The coating process may use all the common coating methods such as spray coating, slit die coating, gravure coating, doctor blade coating, dip coating, and this coating process can be widely understood by those skilled in the art. Detailed description thereof will be omitted herein. Through the coating process, the isolation layer composition is coated on the lithium metal anode, and the solvent component in the separator composition is volatilized to leave a solid separator component on the lithium metal anode.

The step of laminating the separator film on the lithium metal is carried out by producing a film by a conventional method using the separator layer composition.

The negative electrode of the present invention is applicable to both lithium batteries of lithium ion batteries or lithium sulfur batteries. A typical structure of a lithium battery including a negative electrode of the present invention is shown in FIG. 1, and as shown in FIG. 1, an insulating layer coated on the positive electrode 11, the negative electrode 12 of the present invention, and the negative electrode 12 surface. It includes (13), and includes a battery can and a battery packaging film (14) for storing them. In the lithium battery using the negative electrode of the present invention, since the insulating layer is formed on the negative electrode, there is no need to place a separate separator between the positive electrode and the negative electrode. The structure of the cathode coated with the isolation layer of the present invention is shown in FIG. 2. As shown in FIG. 2, the insulating layer 13 is uniformly coated on both surfaces of the cathode 12, and the cathode and the separator have an integral structure.

The positive electrode 11 includes a positive electrode active material capable of an electrochemically reversible oxidation / reduction reaction. The positive electrode active material includes inorganic sulfur (S ₈ ) or a sulfur-based compound. The sulfur-based compound may be selected from the group consisting of Li ₂ S _n (n ≧ 1), an organic sulfur compound and a carbon-sulfur polymer ((C ₂ S _x ) _n : x = 2.5 to 50, n ≧ 2) Can be. Alternatively, a cathode active material of a reversible intercalation / deintercalation material of lithium ions, that is, a lithium metal oxide or a lithium-containing chalcogenide compound may be used as the cathode active material. The lithium metal oxide or the lithium-containing chalcogenide compound is a material capable of reversible intercalation / deintercalation of lithium ions, and means a retired intercalation compound.

The lithium intercalation compound has any one of a monoclinic, hexagonal or cubic structure as a basic structure.

As the lithium intercalation compound used in the present invention, all existing lithium compounds (lithium metal oxides and lithium-containing chalcogenide compounds) may be used, and preferred examples thereof include the following compounds.

[Formula 1]

Li _x Mn _1-y M _y A ₂

[Formula 2]

Li _x Mn _1-y M _y O _2-z X _z

[Formula 3]

Li _x Mn ₂ O _4-z X _z

[Formula 4]

Li _x Mn _2-y M _y A ₄

[Formula 5]

Li _x Co _1-y M _y A ₂

[Formula 6]

Li _x Co _1-y M _y O _2-z X _z

[Formula 7]

Li _x Ni _1-y M _y A ₂

[Formula 8]

Li _x Ni _1-y M _y O _2-z X _z

[Formula 9]

Li _x Ni _1-y Co _y O _2-z X _z

[Formula 10]

Li _x Ni _1-yz Co _y M _z A _α

[Formula 11]

Li _x Ni _1-yz Co _y M _z O _2-α X _α

[Formula 12]

Li _x Ni _1-yz Mn _y M _z A _α

[Formula 13]

Li _x Ni _1-yz Mn _y M _z O _2-α X _α

Wherein 0.90 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, and M is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V or rare earth At least one element selected from the group consisting of elements, A is an element selected from the group consisting of O, F, S and P, and X is F, S or P.)

In addition, the lithium battery of the present invention includes an electrolyte solution containing an electrolytic salt and an organic solvent. The electrolytic salt and the organic solvent are changed according to the type of battery, which is well known to those skilled in the art, so a detailed description thereof will be omitted. For example, when the lithium battery of the present invention is a lithium sulfur battery, a single solvent may be used as the organic solvent, 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 a 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 lithium protective solvents include tetrahydrofuran, dioxolane, 3,5-dimethyl isoxazole, 2,5-dimethyl furan, furan, 2-methyl furan, 1,4-oxane, 4-methyldioxolane, and the like. .

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.

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.

(Example 1)

The isolation layer composition was coated on lithium metal and dried at 80 ° C. to form an isolation layer from which the solvent was removed from the lithium metal to prepare a negative electrode. It was 40% when the porosity of the isolation layer obtained at this time was measured. The isolation layer composition was prepared by adding a silica inorganic material and a polyvinylidene fluoride polymer to an acetone solvent in a weight ratio of 70:30.

Inorganic sulfur (S ₈ ), a carbon black conductive material, and a polyethylene oxide binder were mixed in an acetonitrile solvent at a weight ratio of 6: 2: 2 to prepare a cathode active material slurry. The positive electrode active material slurry was coated on a carbon-coated aluminum (Rexam) current collector and dried to prepare a positive electrode.

A lithium sulfur battery was manufactured in a conventional manner using the positive electrode, the negative electrode, and the electrolyte solution. At this time, as the electrolyte was used dimethoxyethane / 1,3-dioxolane (80/20 volume ratio) in which 1M LiN (SO ₂ CF ₃ ) ₂ dissolved.

The ion conductivity of the prepared isolation layer was measured and found to be 2.310 ^-3 S / cm at room temperature. In addition, after discharging the lithium sulfur battery prepared according to the method of Example 1 to 1.5V at a discharge rate of 0.2C and 110% of the discharge capacity at a charging rate of 0.2C, the cycle life characteristics were measured, and The results are shown in Table 1 below.

Cycles 1 time 10th 50 times 100 times Capacity (mAh) 21.2 17.8 15.1 13.5

  (Example 2)

The isolation layer composition was coated on lithium metal and dried at 80 ° C. to form an isolation layer from which the solvent was removed from the lithium metal to prepare a negative electrode. It was 40% when the porosity of the isolation layer obtained at this time was measured. The isolation layer composition was prepared by adding a zeolide inorganic material and a polyvinyl chloride polymer in an acetone solvent in a weight ratio of 70:30.

Inorganic sulfur (S ₈ ), a carbon black conductive material, and a polyethylene oxide binder were mixed in an acetonitrile solvent at a weight ratio of 6: 2: 2 to prepare a cathode active material slurry. The positive electrode active material slurry was coated on a carbon-coated aluminum (Rexam) current collector and dried to prepare a positive electrode.

A lithium sulfur battery was manufactured in a conventional manner using the positive electrode, the negative electrode, and the electrolyte solution. At this time, as the electrolyte was used dimethoxyethane / 1,3-dioxolane (80/20 volume ratio) in which 1M LiN (SO ₂ CF ₃ ) ₂ dissolved.

The ion conductivity of the prepared isolation layer was measured and found to be 1.910 ^-3 S / cm at room temperature. In addition, after discharging the lithium sulfur battery prepared according to the method of Example 2 to 1.5V at a discharge rate of 0.2C to 110% of the discharge capacity at a charging rate of 0.2C, the cycle life characteristics were measured and the result Is shown in Table 2 below.

Cycles 1 time 10th 50 times 100 times Capacity (mAh) 21.5 17.2 15.3 13.9

(Example 3)

The isolation layer composition was coated on lithium metal and dried at 80 ° C. to form an isolation layer from which the solvent was removed from the lithium metal to prepare a negative electrode. It was 40% when the porosity of the isolation layer obtained at this time was measured. The isolation layer composition was prepared by adding an alumina (Al ₂ O ₃ ) inorganic material having an average particle diameter of 1 micrometer and a polyethylene oxide polymer having a weight average molecular weight of 5,000,000 to an acetonitrile solvent in an 80:20 weight ratio.

Inorganic sulfur (S ₈ ), a carbon black conductive material, and a polyethylene oxide binder were mixed in an acetonitrile solvent at a weight ratio of 6: 2: 2 to prepare a cathode active material slurry. The positive electrode active material slurry was coated on a carbon-coated aluminum (Rexam) current collector and dried to prepare a positive electrode.

A lithium sulfur battery was manufactured in a conventional manner using the positive electrode, the negative electrode, and the electrolyte solution. At this time, as the electrolyte was used dimethoxyethane / 1,3-dioxolane (80/20 volume ratio) in which 1M LiN (SO ₂ CF ₃ ) ₂ dissolved.

Ion conductivity of the prepared isolation layer was measured to be 5.210 ^-3 S / cm at room temperature. When the lithium sulfur battery obtained in Example 1 was discharged to 1.5V at a discharge rate of 0.2C and charged at 110% of the discharge capacity at a charge rate of 0.2C, the cycle life characteristics were measured, and the results are shown in Table 3 below. Indicated.

Cycles 1 time 10th 50 times 100 times Capacity (mAh) 22.5 16.8 17.2 15.9

(Comparative Example 1)

A lithium sulfur battery was manufactured in the same manner as in Example 1, except that Celgard 3501 was used as the lithium metal anode and the separator.

After discharging the lithium sulfur battery prepared according to Comparative Example 1 to 1.5V at a discharge rate of 0.2C and charged at 110% of the discharge capacity at a charge rate of 0.2C, the cycle life characteristics are measured and the results are shown in Table 4 below. Shown in

Cycles 1 time 10th 50 times 100 times Capacity (mAh) 21.5 15.9 7.5 3.2

As described above, the negative electrode for a lithium battery of the present invention has a structure in which lithium metal and a separator are integrated, and the separator and the lithium metal are in uniform physical contact with each other, so that the reaction at the negative electrode occurs uniformly. Can improve.

1 is a perspective view schematically showing a lithium sulfur battery structure of the present invention.

Figure 2 is a perspective view schematically showing the structure of a lithium cathode coated with a separator of the present invention.

Claims (18)

Lithium metal; And An isolation layer including the inorganic material and the polymer formed in the lithium metal in a weight ratio of 50 to 90:50 to 10; A negative electrode for a lithium battery comprising a. The negative electrode of claim 1, wherein the inorganic material is selected from the group consisting of silica, alumina, titanium oxide, zeolite, silicate, and barium titanium oxide. According to claim 1, wherein the polymer is polyvinylidene fluoride-based polymer, polytetrafluoroethylene-based polymer, polyvinyl chloride-based polymer, polyvinyl alcohol-based polymer, polyimide-based polymer and polyethylene oxide-based polymer The negative electrode for lithium batteries which is selected. The negative electrode of claim 1, wherein the isolation layer is a porous isolation layer having a porosity of 20 to 70%. The negative electrode for a lithium battery according to claim 1, wherein the electrode is used in a battery selected from the group consisting of lithium ion batteries and lithium sulfur batteries. Coating the lithium metal with an insulating layer containing inorganic and polymer The manufacturing method of the negative electrode for lithium batteries containing a process. The method of claim 6, wherein the coating process comprises an inorganic material and a polymer in a weight ratio of 50 to 90:50 to 10, liquid-coated the isolation layer composition containing a solvent on the lithium metal, and volatilizing the solvent. The manufacturing method of the negative electrode for lithium batteries. The method of claim 7, wherein the solvent is selected from the group consisting of ether, amide, ester, and alcohol. The method of claim 6, wherein the coating process is performed by directly coating an isolation layer film on the lithium metal. The method of claim 6, wherein the coating step is performed by laminating an isolation layer film on the lithium metal. The method of claim 6, wherein the inorganic material is selected from the group consisting of silica, alumina, titanium oxide, zeolite, silicate and barium titanium oxide. According to claim 6, wherein the polymer is polyvinylidene fluoride-based polymer, polytetrafluoroethylene-based polymer, polyvinyl chloride-based polymer, polyvinyl alcohol-based polymer, polyimide-based polymer and polyethylene oxide-based polymer The manufacturing method of the negative electrode for lithium batteries which is selected.  A negative electrode including a lithium metal, and an isolation layer including an inorganic material and a polymer formed in the lithium metal in a weight ratio of 50 to 90:50 to 10; A positive electrode including a positive electrode active material capable of an electrochemically reversible oxidation / reduction reaction; And Electrolyte Lithium battery comprising a. The lithium battery of claim 13, wherein the inorganic material is selected from the group consisting of silica, alumina, titanium oxide, zeolite, silicate, and barium titanium oxide. The method of claim 13, wherein the polymer is selected from the group consisting of polyvinylidene fluoride polymer, polytetrafluoroethylene polymer, polyvinylchloride polymer, polyvinyl alcohol polymer, polyimide polymer, and polyethylene oxide polymer. The lithium battery which is chosen. The lithium battery of claim 13, wherein the isolation layer is a porous isolation layer having a porosity of 20 to 70%. The method of claim 13, wherein the positive electrode active material capable of occluding and desorbing lithium ions is a lithium-containing chalcogenide compound, elemental sulfur, Li ₂ S _n (n ≥ 1), an organic sulfur compound and a carbon-sulfur polymer ((C ₂ S _x ) _n : lithium battery selected from the group consisting of x = 2.5 to 50, n ≥ 2). The lithium battery of claim 13, wherein the battery is a battery selected from the group consisting of lithium ion batteries and lithium sulfur batteries.