KR102439829B1 - Lithium electrode for lithium secondary battery, preparation methode thereof and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium electrode, a method for manufacturing the same, and a lithium secondary battery including the same. In the lithium electrode according to the present invention, a lithium alloy layer serving as a diffusion barrier of lithium ions and a protective layer protecting lithium metal from the atmosphere are formed on the lithium metal layer, thereby inhibiting the formation of an oxide layer of lithium metal and the growth of lithium dendrites. can

Description

Lithium electrode, manufacturing method thereof, and lithium secondary battery comprising same

The present invention relates to a lithium electrode for improving the performance of a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

Recently, various devices requiring batteries, ranging from mobile phones, wireless home appliances, and electric vehicles, have been developed, and the demand for secondary batteries is also increasing with the development of these devices. In particular, along with the miniaturization trend of electronic products, secondary batteries are also becoming lighter and smaller.

In line with this trend, lithium secondary batteries using lithium metal as an active material have recently been in the spotlight. Lithium metal has a low redox potential (-3.045V with respect to a standard hydrogen electrode) and a high weight energy density (3,860 mAhg ^-1 ), so it is expected as a negative electrode material for high-capacity secondary batteries.

However, when lithium metal is used as a battery negative electrode, a battery is generally manufactured by attaching a lithium foil to a planar current collector. Since lithium is highly reactive as an alkali metal, it reacts explosively with water and also reacts with oxygen in the atmosphere. There is a disadvantage that it is difficult to manufacture and use in a general environment. In particular, when lithium metal is exposed to the atmosphere, it has an oxide film of LiOH, Li ₂ O, Li ₂ CO ₃ , etc. as a result of oxidation. When such an oxide film is present on the surface, the oxide film acts as an insulating film, so that electrical conductivity is lowered, and the smooth movement of lithium ions is inhibited, resulting in an increase in electrical resistance.

For this reason, the vacuum deposition process was performed to form the lithium anode, and the problem of surface oxide film formation due to the reactivity of lithium metal was partially improved, but it is still exposed to the atmosphere during the battery assembly process, so it is impossible to fundamentally suppress the surface oxide film formation. the current situation. Accordingly, there is a need to develop a lithium metal electrode capable of improving energy efficiency by using lithium metal, solving the problem of lithium reactivity, and simplifying the process.

Republic of Korea Patent Publication No. 2017-0124075 "Anode for lithium metal battery and lithium metal battery including the same" Republic of Korea Patent Publication No. 2016-0062025 "Negative electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery and manufacturing method of negative electrode for non-aqueous electrolyte secondary battery"

As described above, the lithium secondary battery has limitations in its manufacturing process due to the reactivity of lithium metal, and when assembling the battery, contact with oxygen and moisture in the atmosphere is unavoidable, so the life and performance of the battery are reduced, and , there is a problem in that the charging and discharging efficiency of the lithium electrode is lowered due to the growth of lithium dendrites. Accordingly, the present inventors have conducted various studies, and as a result, when manufacturing a lithium electrode, a lithium metal layer is not formed directly on the current collector, but a lithium alloy layer and a lithium metal layer are formed on a separate substrate, and then transferred to the current collector to form a lithium electrode. By manufacturing, it was confirmed that it was possible to minimize the situation in which lithium was exposed to the atmosphere during the electrode manufacturing process and to prevent the growth of lithium dendrites, and thus the present invention was completed.

Therefore, it is an object of the present invention to have a structure capable of preventing the growth of lithium dendrites by blocking contact with the atmosphere and lowering the diffusion barrier of lithium metal in the process of forming the lithium electrode of the lithium secondary battery To provide a lithium electrode.

Another object of the present invention is to provide a method for manufacturing a lithium electrode capable of minimizing exposure of lithium metal to the atmosphere during the manufacturing process of the electrode.

Another object of the present invention is to provide a lithium secondary battery including such a lithium electrode.

In order to achieve the above object, the present invention provides a current collector: a lithium metal layer formed on at least one surface of the current collector; and a lithium alloy layer formed on the lithium metal layer.

The lithium alloy layer may include a lithium alloy represented by the following Chemical Formula 1:

<Formula 1>

Li _x M

where x is a real number from 1 to 2.25, and M is selected from the group consisting of In, Au, Ni, Co, Zn, P, Sb, Ag, Pt, Pd, Mn, Si, Mg and Ga.

The thickness of the lithium alloy layer may be 1 nm to 1 μm.

A protective layer may be additionally formed on the lithium alloy layer.

The protective layer is PVDF (Poly Vinylidene Fluoride), PVDF-HFP copolymer (Poly Vinylidene Fluoride-hexafluoroethylne copolymer), PEO (Poly Ethylene Oxide), PMMA (Poly (methyl methacrylate)), cyclo olefin polymer (Cyclo olefin polymer), It may be at least one selected from the group consisting of cyclo olefin copolymer and SBR-CMC (Styrene ButadieneRubber-CarboxymethylCellulose).

The protective layer may have a thickness of 1 nm to 2 μm.

The present invention also

(S1) forming a release layer on at least one surface of the substrate;

(S2) forming a lithium alloy layer on the release layer;

(S3) forming a lithium metal layer on the lithium alloy layer; and

(S4) transferring one surface of the lithium metal layer to be laminated on the current collector; provides a method of manufacturing a lithium electrode comprising.

After the step (S1), (P) may further include the step of forming a protective layer on the release layer.

The release layer may include at least one selected from the group consisting of Si, melamine, and fluorine.

The lithium alloy layer may be formed by evaporation or sputtering.

The lithium metal layer may be formed by evaporation or rolling.

The transfer may be performed by placing the lithium metal layer in contact with at least one surface of the current collector and then pressurizing at 50 to 130° C.

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

According to the present invention, when manufacturing a lithium electrode, the lithium metal layer is not formed directly on the current collector, but a lithium alloy layer and a lithium metal layer are formed on a separate substrate, and then transferred to the current collector to prepare a lithium electrode, thereby producing a lithium electrode during the electrode manufacturing process. It is possible to minimize the situation in which lithium is exposed to the atmosphere and prevent the growth of lithium dendrites.

In addition, by forming the lithium alloy layer to an appropriate thickness, it is possible to improve the lifespan characteristics of the battery.

1 is a longitudinal cross-sectional view of a lithium electrode according to an embodiment of the present invention.
2 is a longitudinal cross-sectional view of a lithium electrode according to another embodiment of the present invention.
3 is a longitudinal cross-sectional view of a lithium electrode during a manufacturing process of a lithium electrode according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms, and is not limited thereto.

In the drawings, in order to clearly explain the present invention, parts irrelevant to the description are omitted, and similar reference numerals are used for similar parts throughout the specification. In addition, the sizes and relative sizes of components shown in the drawings are independent of actual scale, and may be reduced or exaggerated for clarity of description.

lithium electrode

The present invention is a lithium electrode having a structure that prevents the formation of an oxide layer (native layer) by minimizing exposure of lithium metal to the atmosphere during a lithium electrode manufacturing process or after manufacturing is completed, and serves as a lithium ion diffusion barrier (diffuser layer). it's about

Hereinafter, a lithium electrode according to the present invention will be described in more detail with reference to the drawings.

1 is a longitudinal sectional view of a lithium electrode according to an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of a lithium electrode according to another embodiment of the present invention.

Referring to FIG. 1 , the lithium electrode of the present invention may include a current collector 10 , a lithium metal layer 20 formed on both sides of the current collector 10 , and a lithium alloy layer 30 formed on the lithium metal layer 20 . can In FIG. 1 , only the case in which the lithium metal layer 20 is formed on both surfaces of the current collector 10 is illustrated, but the lithium metal layer 20 may be formed on one surface of the current collector 10 .

Also, referring to FIG. 2 , a protective layer 40 may be additionally formed on the lithium alloy layer 30 .

The current collector 10 may be a current collector selected from the group consisting of copper (Cu), aluminum (Al), nickel (Ni), titanium (Ti), sintered carbon and stainless steel (SUS), but is limited thereto It is not, and it is possible to use a wide range of current collectors used in the production of electrodes in the art.

The thickness of the current collector 10 may be 1 to 10 μm, preferably 1 to 8 μm, more preferably 1 to 6 μm, and if the thickness of the current collector 10 is less than the above range, the durability of the electrode is reduced may be, and if it exceeds the above range, the thickness of the electrode may be increased.

The lithium metal layer 20 is formed on both sides of the current collector, and since the lithium metal layer 20 is formed on both sides of the current collector 10 by a transfer process by a manufacturing method as described below, rather than being formed by deposition, it is thin and thin. It is possible to form a uniform lithium metal layer 20 .

In addition, since the lithium metal layers 20 respectively formed on both surfaces of the current collector 10 are transferred after being formed by a process under the same conditions, the two lithium metal layers 20 may have the same shape and physical properties.

The lithium metal layer 20 may have a thickness of 0.1 to 50 μm, preferably 5 to 40 μm, more preferably 10 to 30 μm, and if it is less than the above range, the charge/discharge performance of the battery is reduced, and if it exceeds the above range There may be a problem in that the thickness of the electrode is increased.

In a typical lithium secondary battery, since the amount of lithium contained in the positive electrode is all, the capacity is limited. However, in the case of the battery including the lithium electrode according to the present invention as the negative electrode, lithium is included in the negative electrode as well as the positive electrode, and lithium ions can be supplied from these lithium, so that an additional increase in capacity can be expected. In the lithium anode, if the thickness of the lithium metal layer is thick, the capacity increase will be greater, but in consideration of economy and handling, the lithium metal layer having a thickness in the numerical range as described above is preferable.

The lithium alloy layer 30 may serve as a diffusion barrier for lithium ions to prevent the growth of lithium dendrites, and may include a lithium alloy represented by the following Chemical Formula 1 .

<Formula 1>

Li _x M

where x is a real number from 1 to 2.25, and M is selected from the group consisting of In, Au, Ni, Co, Zn, P, Sb, Ag, Pt, Pd, Mn, Si, Mg and Ga.

Preferably, M in Formula 1 may be selected from Al, Ni, Mg, and Au, which means that metals having a low calculated value of the Li diffusion barrier on each metal surface have a low diffusion barrier of Li ions, so that This is because uniform plating is well formed.

In Chemical Formula 1, M, which is a metal capable of forming an alloy with lithium, reacts with Li to form an alloy phase. That is, the interface with Li metal is the alloy phase, and each metal is present in the outermost layer. That is, it is in the form of Li/Li-M alloy/M, and the alloy layer of this Li-M alloy/M does not have clear boundaries to form one layer, and the outermost layer of the alloy layer is in the form in which each metal is located. can

The thickness of the lithium alloy layer 30 may be 1 nm to 1 μm, preferably 1 nm to 500 nm, more preferably 1 nm to 100 nm, and if it is less than the above range, the lithium dendrite inhibitory effect is insignificant, If it exceeds the above range, the difference in density with Li is large, so that the surface and the interface of the Li metal are not maintained and peeling may occur.

The protective layer 40 minimizes the formation of a surface oxide film (native layer) by protecting the lithium metal from an external environment such as moisture or outside air during a series of processes for manufacturing the lithium electrode 100 and the driving process of the lithium electrode 100 . can do.

Therefore, the material forming the protective layer 40 should have high moisture barrier performance, stability to the electrolyte, high electrolyte moisture content, and excellent oxidation/reduction stability.

The protective layer 40 is PVDF (Poly Vinylidene Fluoride), PVDF-HFP copolymer (Poly Vinylidene Fluoride-hexafluoroethylne copolymer), PEO (Poly Ethylene Oxide), PMMA (Poly (methyl methacrylate)), cyclo olefin polymer (Cyclo olefin polymer) ), cyclo olefin copolymer, and SBR-CMC (Styrene ButadieneRubber-CarboxymethylCellulose) may include at least one selected from the group consisting of.

The thickness of the protective layer 40 may be 1 nm to 2 μm, preferably 5 nm to 1.5 μm, and more preferably 10 nm to 1 μm. If it is less than the above range, the function of protecting the lithium metal from moisture or external air may be reduced, and if it exceeds the above range, the manufactured lithium electrode 100 may be thickened.

Lithium electrode manufacturing method

The present invention also uses a transfer process to prevent the formation of a native layer of lithium metal during the manufacturing process of the lithium electrode.

A method for manufacturing a lithium electrode according to the present invention comprises the steps of (S1) forming a release layer on both surfaces of a substrate; (S2) forming a lithium alloy layer on the release layer; (S3) forming a lithium metal layer on the lithium alloy layer; and (S4) transferring one surface of the lithium metal layer to be laminated on the current collector.

In addition, after the step (S1) (P) may further include the step of forming a protective layer on the release layer. When the protective layer is formed, a lithium alloy layer may be formed on the protective layer in step (S2).

Hereinafter, with reference to the drawings, the manufacturing method of the lithium electrode according to the present invention in each step will be described in more detail.

3 is a longitudinal cross-sectional view of a lithium electrode during a manufacturing process of a lithium electrode according to an embodiment of the present invention.

(S1) step

In step (S1), the release layer 50 may be formed on at least one surface of the substrate 60 , for example, on both surfaces of the substrate 60 .

The substrate 60 can withstand process conditions such as high temperature in the step of depositing the lithium metal, and the lithium metal layer 20 is the current collector during the winding process for transferring the deposited lithium metal layer 20 to the current collector. It may have a feature capable of preventing the reverse peeling problem transferred onto the substrate 60 other than (10).

For example, the substrate 60 may include polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate, PMMA), cellulose tri-acetate (TAC), and poly It may be at least one selected from the group consisting of propylene (Polypropylene), polyethylene (Polyethylene) and polycarbonate (Polycarbonate).

The substrate 60 may have a release layer 50 formed on at least one surface, and preferably a release layer 50 formed on both surfaces thereof. Reverse peeling in which the lithium metal layer 20 is transferred onto the substrate 60 rather than the current collector 10 during the winding process for transferring the deposited lithium metal layer 20 to the current collector 10 due to the release layer 50 Problems can be prevented, and the substrate 60 can be easily separated after the lithium metal layer 20 is transferred onto the current collector 10 .

The release layer 50 may include at least one selected from the group consisting of Si, melamine, and fluorine.

The release layer 50 may be formed by a coating method, for example, the coating method includes dip coating, spray coating, spin coating, die coating, and It may be a method selected from the group consisting of roll coating, but is not limited thereto, and various coating methods that can be used to form a coating layer in the art may be used.

The thickness of the release layer 50 may be 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm, and more preferably 0.1 μm to 0.5 μm. If it is less than the above range, a reverse peeling problem may occur during the transfer process, and if it exceeds the above range, it may be difficult to proceed with the process at the time of peeling the release layer after the transfer process.

(P) step

In step (P), the protective layer 40 may be formed on the release layer 50 .

The protective layer 40 may be formed by coating.

As a coating method for forming the protective layer 40, dip coating, spray coating, spin coating, die coating, roll coating, slot die Select from the group consisting of slot-die coating, bar coating, gravure coating, comma coating, curtain coating and micro-gravure coating It may be a method that can be used, but is not limited thereto, and various coating methods that can be used to form a coating layer in the art can be used.

The coating solution for forming the protective layer 40 may be prepared by dissolving the polymer for forming the protective layer as described above in a solvent, in this case, the concentration of the coating solution is 1% to 20%, preferably 3% to 10 %, more preferably 4% to 8%. If the concentration of the coating solution is less than the above range, the viscosity is very low and the coating process is difficult to proceed. At this time, as a solvent for forming the coating solution, NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl Formamide), DMAc (Dimethyl Acetamide), Tetramethyl Urea, DMSO (Dimethyl Sulfoxide) and triethyl phosphate (Triethyl Phosphate) It may be one or more selected from the group consisting of, in particular, when using NMP, the solubility of the polymer for forming the protective layer as described above is high, and it may be advantageous to form the protective layer 40 by the coating process.

Characteristics such as material and thickness of the protective layer 40 are the same as described above.

(S2) step

In step (S2), the lithium alloy layer 30 may be formed on the release layer 50 . When the protective layer 40 is formed in the step (P), the lithium alloy layer 30 may be formed on the protective layer 40 .

The lithium alloy layer 30 may be formed by a deposition or sputtering process.

A deposition method for depositing the lithium alloy may be selected from vacuum deposition, chemical vapor deposition, chemical vapor deposition (CVD), and physical vapor deposition. It is not limited, and various deposition methods used in the art may be used.

Characteristics such as material and thickness of the lithium alloy layer 30 are the same as described above.

(S3) step

In step (S3), the lithium metal layer 20 may be formed on the lithium alloy layer 30 .

The lithium metal layer 20 may be formed by a deposition or rolling process.

A deposition method for depositing lithium metal may be selected from vacuum deposition, chemical vapor deposition, chemical vapor deposition (CVD), and physical vapor deposition. It is not limited, and various deposition methods used in the art may be used.

(S4) step

(S4) transferring one surface of the lithium metal layer 20 to be laminated on the current collector 10

The transfer is performed by winding the structure in which the substrate 60, the release layer 50, the protective layer 40, the lithium alloy layer 30, and the lithium metal layer 20 are sequentially stacked, and then collecting it using a device such as a roll press. The lithium metal layer may be transferred onto the entire 10 .

In general, when the lithium metal is directly deposited on the current collector, in particular, when the lithium metal is directly deposited on the copper current collector, there is a problem that the copper current collector is easily broken, but the present invention provides a lithium metal layer (20) After forming the lithium electrode 100 by transferring the formed lithium metal layer 20 itself onto the current collector, the lithium electrode 100 can be manufactured using various current collectors.

The present invention provides a negative electrode for a lithium secondary battery comprising a lithium electrode on at least one surface of a current collector, wherein the lithium electrode has a surface oxide film (native layer) having a thickness of 15 to 50 nm.

A lithium electrode manufactured by a conventional method generates a surface oxide film of about several hundred nm on the surface, and in order to prevent this, even when the lithium electrode is manufactured by a deposition process in a vacuum, the formation of a surface oxide film of about 100 nm is inevitable.

Such a surface oxide film is generated by exposing the lithium electrode to the air. In the present invention, the lithium electrode is prevented from being exposed to oxygen and moisture in the air before the process of laminating the lithium electrode to the copper current collector, so that the surface oxide film is formed. can be minimized

1 is a cross-sectional view of a lithium electrode including a surface oxide film according to the present invention. Referring to FIG. 1 , the surface oxide film 120 is formed on one surface of the lithium electrode 100 not in contact with the current collector 200 , and the lithium electrode 100 is the surface oxide film 120 is Li ₂ O. a first oxide layer 121 including; a second oxide layer 122 including Li ₂ O and LiOH; and a third oxide layer 123 including Li ₂ O, LiOH, and Li ₂ CO ₃ .

The first oxide layer 121 to the third oxide layer 123 do not have a critical plane, but are arbitrarily partitioned according to the distribution of the oxide composition. In this case, Li ₂ O, LiOH, and Li ₂ CO ₃ are formed at different depths from the outermost surface of the lithium electrode 100 , and their depth is in the order of Li ₂ O > LiOH > Li ₂ CO ₃ .

More specifically, the distance from the outermost surface to the point where Li ₂ O exists is defined as the first oxide layer 121, and the thickness thereof may be 10 to 30 nm, preferably 8 to 20 nm. In addition, the distance from the outermost layer to the point where LiOH exists is defined as the second oxide layer 122, and the thickness thereof may be 4 to 15 nm, preferably 3 to 10 nm. In addition, the distance from the outermost layer to the point where Li ₂ CO ₃ exists is defined as the third oxide layer 123 , and the thickness thereof may be 1 to 5 nm, preferably 0.5 to 3 nm.

The lithium metal layer 110 is a layer remaining after the surface oxide film 120 is formed in the lithium electrode 100 , and refers to a metal layer including a lithium metal element. The material of the lithium metal layer may be a lithium alloy, a lithium metal, an oxide of a lithium alloy, or a lithium oxide. As a non-limiting example, the negative electrode may be a thin film of lithium metal, and lithium and at least one metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and Sn. It may be an alloy with In this case, in addition to the surface oxide layer 120 , the lithium metal layer 110 may be partially altered by oxygen or moisture or may contain impurities.

The thickness of the lithium electrode 100 including the lithium metal layer 110 and the surface oxide film 120 may be 0.01 to 100 μm, preferably 0.05 to 75 μm, and more preferably 0.1 to 50 μm. . If the thickness is less than 0.01 μm, it is difficult to satisfy cycle characteristics due to insufficient lithium efficiency, and if it exceeds 100 μm, a problem of energy density decrease due to an increase in lithium thickness occurs.

Specifically, the transfer process may be carried out at room temperature after positioning the lithium metal layer 20 on at least one surface of the current collector 10 so that it is in contact, and when carried out at a high temperature, 50 to 130° C., preferably 60 to It can be carried out by pressing and laminating in a roll press at 120 ° C., more preferably at 70 to 100 ° C. At this time, if the temperature is less than the above range, the adhesion between the respective layers may be reduced during lamination, and if the temperature is above the above range, the physical properties of each layer may be deformed.

In addition, after the transfer process, a process of peeling the substrate 60 on which the release layer 50 is formed may be further included.

lithium secondary battery

The positive electrode according to the present invention may be prepared in the form of a positive electrode by forming a film on a positive electrode current collector by forming a composition including a positive electrode active material, a conductive material, and a binder.

The positive active material may vary depending on the use of the lithium secondary battery, and a known material is used for a specific composition. For example, any one lithium transition metal oxide selected from the group consisting of lithium cobalt oxide, lithium manganese oxide, lithium copper oxide, lithium nickel oxide and lithium manganese composite oxide, and lithium-nickel-manganese-cobalt oxide. and, more specifically, Li _{1 + x} Mn _{2 -x} O ₄ (where _x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , such as lithium manganese oxide; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; LiNi _{1 - x} M _x O ₂ (wherein M=Co, Mn, Al, Cu,Fe, Mg, B or Ga, and x=0.01 to 0.3 lithium nickel oxide); LiMn _{2 - x} MxO ₂ (wherein M=Co, Ni, Fe, Cr, Zn or Ta and x=0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M=Fe, Co, Ni, Cu) or Zn), a lithium manganese composite oxide, Li(Ni _a Co _b Mn _c )O ₂ (here, 0 < a < 1, 0 < b < 1, 0 < c < 1, a+b+c =1) a lithium-nickel-manganese-cobalt-based oxide, Fe ₂ (MoO ₄ ) ₃ ; elemental sulfur, a disulfide compound, an organosulfur compound, and a carbon-sulfur polymer ((C ₂ S _x ) _n : x=2.5 to 50, n≥≥2); graphite-based materials; carbon black-based materials such as Super-P, Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, Summer Black, and Carbon Black; carbon derivatives such as fullerene; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; and conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole; A catalyst such as Pt or Ru may be supported on a porous carbon support, and the like, but is not limited thereto.

The conductive material is a component for further improving the conductivity of the positive electrode active material, and includes, without limitation, graphite such as natural graphite or 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 fibers and metal fibers; 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 may be used.

The positive electrode may further include a binder for bonding the positive electrode active material and the conductive material and bonding to the current collector. The binder may include a thermoplastic resin or a thermosetting resin. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkylvinylether copolymer, vinylidene fluoride-hexa Fluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoro Loethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene -Acrylic acid copolymer and the like may be used alone or in combination, but it is not necessarily limited thereto, and any one that can be used as a binder in the art is possible.

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

The positive electrode as described above can be manufactured according to a conventional method, and specifically, a composition for forming a positive electrode active material layer prepared by mixing a positive electrode active material, a conductive material, and a binder in an organic solvent is applied and dried on a current collector, and optionally In order to improve the electrode density, it may be manufactured by compression molding on the current collector. In this case, as the organic solvent, the positive electrode active material, the binder, and the conductive material can be uniformly dispersed, and it is preferable to use one that is easily evaporated. Specific examples thereof include acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol.

The positive electrode composition may be coated on the positive electrode current collector using 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 court method, a die coating method, a comma coating method, or a mixture thereof may be used in various ways.

The positive electrode and the positive electrode composition subjected to the coating process are then dried through evaporation of the solvent or dispersion medium, the density of the coating film, and the adhesion between the coating film and the current collector. At this time, drying is carried out according to a conventional method, and this is not particularly limited.

A conventional separator may be interposed between the positive electrode and the negative electrode. The separator is a physical separator having a function of physically separating the electrodes, and can be used without any particular limitation as long as it is used as a conventional separator, and in particular, it is preferable to have low resistance to ion movement of the electrolyte and excellent electrolyte moisture content.

In addition, the separator enables transport of lithium ions between the positive electrode and the negative electrode while separating or insulating the positive electrode and the negative electrode from each other. Such a separator may be made of a porous, non-conductive or insulating material. The separator may be an independent member such as a film, or a coating layer added to the positive electrode and/or the negative electrode.

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

The nonwoven fabric may include, for example, polyphenyleneoxide, polyimide, polyamide, polycarbonate, polyethyleneterephthalate, polyethylenenaphthalate, in addition to the polyolefin-based nonwoven fabric described above. , polybutyleneterephthalate, polyphenylenesulfide, polyacetal, polyethersulfone, polyetheretherketone, polyester, etc. alone or Nonwoven fabrics formed of polymers mixed with these are possible, and such nonwoven fabrics are in the form of fibers forming a porous web, and include a spunbond or meltblown form composed of long fibers.

The thickness of the separator is not particularly limited, but is preferably in the range of 1 to 100 μm, and more preferably in the range of 5 to 50 μm. When the thickness of the separator is less than 1 μm, mechanical properties cannot be maintained, and when it exceeds 100 μm, the separator acts as a resistance layer, and thus the performance of the battery is deteriorated.

The pore size and porosity of the separation membrane are not particularly limited, but preferably have a pore size of 0.1 to 50 μm, and a porosity of 10 to 95%. When the pore size of the separator is less than 0.1 μm or the porosity is less than 10%, the separator acts as a resistance layer, and when the pore size exceeds 50 μm or the porosity exceeds 95%, mechanical properties cannot be maintained .

The electrolyte of the lithium secondary battery is a lithium salt-containing electrolyte, which may be an aqueous or non-aqueous non-aqueous electrolyte, and is preferably a non-aqueous electrolyte composed of an organic solvent electrolyte and a lithium salt. In addition, an organic solid electrolyte or an inorganic solid electrolyte may be included, but the present invention is not limited thereto.

As the lithium salt, those commonly used in electrolytes for lithium secondary batteries may be used without limitation. For example, as an anion of the lithium salt, F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ -, PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , ( from the group consisting of CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- It may include any one selected or two or more of them.

As the organic solvent included in the non-aqueous electrolyte, those commonly used in electrolytes for lithium secondary batteries may be used without limitation, for example, ethers, esters, amides, linear carbonates, cyclic carbonates, etc. individually or two or more types. It can be used by mixing. Among them, cyclic carbonates, linear carbonates, or a carbonate compound that is 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, There is any one selected from the group consisting of 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of these halides include, but are not limited to, fluoroethylene carbonate (FEC).

In addition, specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, or these A mixture of two or more of them may be typically used, but is not limited thereto.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so that lithium salts in the electrolyte can be more easily dissociated. If a low-viscosity, low-dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having a higher electrical conductivity can be prepared.

In addition, as the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether and ethylpropyl ether or a mixture of two or more thereof may be used. , but is not limited thereto.

And esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ - Any one selected from the group consisting of -valerolactone and ε-caprolactone or a mixture of two or more thereof may be used, but the present invention is not limited thereto.

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

The lithium secondary battery according to the present invention is capable of lamination, stacking, and folding processes of a separator and an electrode in addition to winding, which is a general process. In addition, the battery case may be of a cylindrical shape, a square shape, a pouch type, or a coin type.

At this time, the lithium secondary battery can be classified into a variety of batteries, such as a lithium-sulfur battery, a lithium-air battery, a lithium-oxide battery, and a lithium all-solid-state battery, depending on the type of anode material and separator used. The lithium secondary battery may be classified into a cylindrical shape, a square shape, a coin type, a pouch type, etc. depending on the shape of the case, and depending on the shape accommodated in the case, for example, a jelly-roll type, a stack type, a stack-folding type (stack- Z-folding type included), or lamination-stack type. In addition, according to the size of the lithium secondary battery, it can be divided into a bulk type and a thin film type. Since the structure and manufacturing method of these batteries are well known in the art, a detailed description thereof will be omitted.

The lithium secondary battery according to the present invention can be used as a power source for devices requiring high stability. Specific examples of the device include a power tool that moves by being powered by an omniscient motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; Electric golf carts; and a power storage system, but is not limited thereto.

After manufacturing the electrode assembly in which the positive electrode, the separator, and the negative electrode are sequentially stacked, the electrode assembly is placed in a battery case, and then an electrolyte is injected and sealed with a cap plate and a gasket to manufacture a lithium secondary battery.

At this time, the lithium secondary battery 10 can be classified into various batteries such as lithium-sulfur batteries, lithium-air batteries, lithium-oxide batteries, lithium all-solid batteries, etc. , coin type, pouch type, and the like, and can be divided into bulk type and thin film type according to the size. Since the structure and manufacturing method of these batteries are well known in the art, a detailed description thereof will be omitted.

The lithium secondary battery according to the present invention can be used as a power source for devices requiring high capacity and high rate characteristics. Specific examples of the device include a power tool powered by an omniscient motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles including electric bicycles (e-bikes) and electric scooters; electric golf carts; and a power storage system, but is not limited thereto.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It goes without saying that such variations and modifications fall within the scope of the appended claims.

Example One

(1) Preparation of lithium electrode

As a substrate, a release PET film (SKC Haas RX12G 50 μm) having a release layer formed on both sides was prepared.

5 nm of Al metal was deposited on the release layer of the release PET film. A lithium metal layer having a thickness of 20 μm was formed by depositing a lithium metal on the Al to form a structure in which a base material having a release layer, a lithium alloy layer, and a lithium metal layer are sequentially stacked.

The laminated structure was wound at a speed of 1 m/min.

Thereafter, the lithium metal layer was transferred onto the Cu current collector by using a roll press equipment to prepare a lithium electrode having a thickness of 20 μm in which the Cu current collector, the lithium metal layer, and the lithium alloy layer were sequentially stacked.

(2) Manufacture of lithium secondary battery

A positive electrode was prepared using LCO (LiCoO ₂ ) as a positive electrode active material. A slurry was prepared by mixing N-methylpyrrolidone (NMP) as a solvent, LCO: Super-P: PVDF = 95: 2.5: 2.5 by weight, and coated on an aluminum foil having a thickness of 12 μm to 70 μm. A thick anode was prepared.

Using the electrode prepared in (1) as a negative electrode, polyethylene having a thickness of 20 μm was interposed between the positive electrode and the negative electrode as a separator, and then, ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = A lithium secondary battery was prepared by injecting an electrolyte containing LiPF ₆ 1.0 M as a lithium salt and 2 wt% of vinylene carbonate (VC) as an additive into a 1:2:1 (v/v) solvent.

Example 2

The same procedure as in Example 1 was performed, except that a protective layer was further formed on the release layer to prepare (1) a lithium electrode having a thickness of 20 μm and (2) a lithium secondary battery.

At this time, a PVDF-HFP coating solution was prepared as a coating solution for forming a protective layer. The PVDF-HFP coating solution was obtained by dissolving PVDF-HFP (LBG Grade from Arkema Corporation) in an NMP solvent to obtain a 5% solution.

A PVDF-HFP protective layer was formed by coating the PVDF-HFP coating solution with a thickness of 0.5 μm on one surface of the release PET film using a Micro-Gravure coater.

Example 3

The same procedure as in Example 1 was performed, except that 0.5 nm of Al metal was deposited on the release layer of the release PET film to prepare a lithium electrode.

Example 4

The same procedure as in Example 1 was performed, except that 3 μm of Al metal was deposited on the release layer of the release PET film to prepare a lithium electrode.

Comparative Example 1

A lithium electrode having a thickness of 20 μm in which a Cu current collector and a lithium metal layer were laminated was prepared in the same manner as in Example 1, but without forming a lithium alloy layer.

Experimental example One

The thickness of the lithium alloy layer and the protective layer of Examples 1 to 4 and Comparative Example 1 was analyzed using X-ray photoelectron spectroscopy (XPS), and the results are shown in Table 1 below.

lithium alloy layer thickness protective layer thickness Example 1 5 nm - Example 2 5 nm 500 nm Example 3 0.5 nm - Example 4 3 μm - Comparative Example 1 - -

Referring to Table 1, it can be seen that the total thickness of the surface oxide layer is thin in the order of Comparative Example 1 > Comparative Example 2 > Example 1, and the first to third oxide layers show the same tendency.

Experimental example 2

In order to confirm the lifespan characteristics of the lithium secondary battery including the lithium electrode prepared in Examples and Comparative Examples, a charge/discharge cycle experiment was performed, and the experimental conditions were as follows.

Charge: rate 0.2C, voltage 4.25V, CC/CV (5% currentcutat 1C)

Discharge: rate 0.5C, voltage 3V, CC

The number of cycles when the discharge capacity reached 80% compared to the initial capacity of the battery was measured while repeating the cycle under the above conditions, and the results are shown in Table 2 below.

Number of cycles to reach 80% of discharge capacity Example 1 321 Example 2 345 Example 3 198 Example 4 not rated Comparative Example 1 195

Referring to Table 2, in the case of the lithium electrodes of Examples 1 to 3, the lifespan characteristics are improved compared to Comparative Example 1 which does not include a lithium alloy layer, including a Cu current collector, a lithium metal layer, and a lithium alloy layer. Able to know.

However, in the case of Example 3, since the thickness of the lithium alloy layer is relatively thin, the effect of improving the lifespan characteristics is rather insignificant.

In addition, in the case of Example 4, since the thickness of the lithium alloy layer was relatively thick, and the lithium was peeled off during the manufacturing process, it was impossible to evaluate the battery.

The reason for the exfoliation is that the interface between the two materials is not maintained because the difference in density between the deposited lithium metal and the lithium alloy is large.

It can be seen that the lithium electrode protected by the release coating film according to the present invention has improved lifespan characteristics by about 2 to 4 times. Therefore, it can be seen that the thickness of the surface oxide layer is closely related to the lifespan characteristics of the battery, and it is confirmed that the battery life characteristics are improved when the thickness of the surface oxide layer is reduced.

100: lithium electrode
10: current collector
20: lithium metal layer
30: lithium alloy layer
40: protective layer
50: release layer
60: description

Claims (12)

delete delete delete delete delete (S1) forming a release layer on both sides of the substrate;
(S2) forming a lithium alloy layer on the release layer;
(S3) forming a lithium metal layer on the lithium alloy layer; and
(S4) After winding the structure formed by sequentially stacking the base material, the release layer, the lithium alloy layer and the lithium metal layer, using a roll press, the structure is used as a current collector so that the lithium metal layer of the structure is laminated on the current collector A method of manufacturing a lithium electrode comprising; transferring. 7. The method of claim 6,
After step (S1)
(P) A method of manufacturing a lithium electrode further comprising the step of forming a protective layer on the release layer. 7. The method of claim 6,
The release layer is a method of manufacturing a lithium electrode comprising at least one selected from the group consisting of Si, melamine and fluorine. 7. The method of claim 6,
The lithium alloy layer is a method of manufacturing a lithium electrode formed by deposition (evaporation) or sputtering (sputtering). 7. The method of claim 6,
The lithium metal layer is a method of manufacturing a lithium electrode formed by evaporation (evaporation) or rolling. 7. The method of claim 6,
the warrior
A method of manufacturing a lithium electrode, wherein the lithium metal layer is placed in contact with at least one surface of the current collector and laminated by pressing at 50 to 130°C. delete

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