KR20190143710A - Curent Collector, Electrode and Lithium Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to a current collector, a lithium electrode comprising the same, and a lithium secondary battery. More specifically, in a three-dimensional structure current collector with pores formed therein, seed metal is deposited on an upper surface facing a separator and a lower surface on the opposite side to allow the lower surface to have a lower reduction potential than that of the lower surface, thereby moving lithium ions to the lower surface of the three-dimensional structure current collector to prevent the growth of lithium dendrites.

Description

Current collector, electrode and lithium secondary battery comprising same {Curent Collector, Electrode and Lithium Secondary Battery Comprising the Same}

The present invention relates to a current collector, an electrode including the same, and a lithium secondary battery.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. The electrochemical device is the area that is receiving the most attention in this respect, and the development of a secondary battery capable of charging and discharging has been the focus of attention, and in recent years in the development of such a battery in order to improve the capacity density and specific energy R & D on the design of electrodes and batteries is underway.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have a higher operating voltage and greater energy density than conventional batteries such as Ni-MII, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.

In general, a lithium secondary battery is embedded in a battery case in 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 stacked or wound, and the nonaqueous electrolyte is injected therein.

At this time, when using a lithium electrode as said negative electrode, the lithium electrode formed by attaching a lithium foil on the planar collector generally has been used. However, as the high capacity and long life of the lithium secondary battery are required, a current collector having a three-dimensional structure has been developed to improve the capacity of the lithium secondary battery and to suppress a decrease in capacity during repeated charge and discharge cycles. .

Korean Patent Laid-Open Publication No. 2002-0088417 relates to a lithium electrode using a porous three-dimensional structure current collector, by uniformly distributing lithium or lithium alloy in the pores of the porous three-dimensional structure current collector, It is described that performance can be improved.

However, such a conventional three-dimensional structure current collector has a problem that the lithium is reduced at the surface of the current collector to block pores of the surface, thereby preventing the use of the interior of the three-dimensional structure current collector, and thus cannot take advantage of the three-dimensional structure. There was this.

Therefore, when the three-dimensional structure current collector having pores is applied to a lithium secondary battery, it is required to develop a technology capable of solving the problem of growing lithium dendrites by blocking pores distributed on the surface of the three-dimensional structure current collector.

Korean Laid-Open Patent No. 2002-0088417 (2002.11.27)

Accordingly, the present inventors conducted various studies to solve the above problems, and as a result, by depositing a seed metal on the bottom of the three-dimensional structure current collector with pores, compared to the top of the three-dimensional structure current collector The three-dimensional structure current collector was manufactured so that the lower surface showed a low reduction potential. Such a three-dimensional structure current collector has been confirmed that lithium ions move to the lower surface of the three-dimensional structure current collector due to the reduction potential difference between the upper and lower surfaces, thereby preventing the growth of lithium dendrites.

Accordingly, it is an object of the present invention to provide a current collector and a method of manufacturing the same in which growth of lithium dendrites can be prevented.

Another object of the present invention is to provide an electrode including the current collector.

Still another object of the present invention is to provide a lithium secondary battery including an electrode including the current collector.

In order to achieve the above object, the present invention provides a current collector having a three-dimensional structure, the metal is formed on one surface.

The metal may be a metal particle.

The metal may be one or more selected from the group consisting of Au, Zn, Mg, Ag, Al, Pt, Si, Ca, and alloys thereof.

The metal may be deposited on one surface of the current collector.

The current collector may include an upper surface facing the separator and a lower surface disposed on an opposite side of the upper surface, and the metal may be formed on the lower surface.

The current collector may include one or more selected from the group consisting of Al, Cu, Zn, Au, Ag, In, Mg, Ni, and alloys thereof.

The porosity of the current collector may be 50 to 90%.

The thickness of the current collector may be 20 to 200 μm.

The present invention also provides an electrode comprising the current collector.

The present invention also provides a lithium secondary battery including a positive electrode, a negative electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, wherein the negative electrode includes the current collector, the current collector is opposite to the upper surface facing the separator The metal is formed on the lower surface provided in, to provide a lithium secondary battery.

According to the present invention, in the three-dimensional structure current collector with pores, due to the seed metal deposited on the lower surface opposite to the upper surface facing the separator, the lower surface has a lower reduction potential than the upper surface. Accordingly, due to the potential difference between the upper and lower surfaces of the three-dimensional structure current collector, lithium ions move to the lower surface of the current collector, thereby preventing the growth of lithium dendrites.

In addition, since growth of lithium dendrites is prevented in the three-dimensional structure current collector according to the present invention, when the three-dimensional structure current collector is applied to a lithium secondary battery, battery performance such as cycle life may be improved.

1 shows a schematic diagram of a current collector according to the present invention.
2 is a schematic diagram showing a partial structure of a lithium secondary battery according to the present invention.

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

As used herein, the top of the three-dimensional structure current collector as one surface of the three-dimensional structure current collector, means a surface facing the separator.

As used herein, the bottom of the three-dimensional structure current collector is the other surface of the three-dimensional structure current collector, which means a surface facing the separator, that is, the opposite surface of the upper surface.

House

The present invention has a three-dimensional structure, and relates to a current collector having a metal formed on one surface. The three-dimensional structure may be formed by pores.

1 shows a schematic diagram of a current collector according to the present invention.

Referring to FIG. 1, the three-dimensional structure current collector 10 may include two surfaces, that is, an upper surface 11 and a lower surface 12, and a metal 13 may be formed on the lower surface 12. In this case, the upper surface 11 and the lower surface 12 are divided according to whether or not facing the separator when the current collector 10 is applied to the battery as defined above.

The metal 13 is formed only on the lower surface 12 of the three-dimensional structure current collector 10, and less energy is required when Li is reduced and produced in the metal 13 than the current collector during nuclear growth. Li is reduced first. At this time, a potential difference between Li generated on the lower surface and the upper surface is generated, and lithium ions are moved to the lower surface 12 of the three-dimensional structure current collector 10 by the potential difference between the upper surface 11 and the lower surface 12. The metal 13 may be referred to as a seed metal that induces the movement and growth of lithium ions. For example, the potential difference may be 3V to 3.5V based on Li generated on the lower surface.

The metal 13 may be in the form of metal particles deposited on the bottom surface 12 of the three-dimensional structure current collector 10.

The metal 13 is a metal having a small overvoltage with the electrode active material as compared with the electrode current collector; Or a metal having a multiphase with the electrode active material.

For example, when the electrode active material is lithium metal, a metal having a low overvoltage compared to Cu (current collector) when forming a lithium metal has a low interfacial energy when reacting with lithium metal or a diffusion energy barrier of Li ions on the metal surface. As a metal that is equal to or less than Li, the metal may be at least one selected from the group consisting of Au, Zn, Mg, Ag, Al, Pt, In, Co, Ni, Mn, and Si, and may be multiphase with the lithium metal. The metal having) may be Ca as a metal having a plurality of sites capable of reacting with lithium metal, but is not limited thereto. Preferably the metal 13 may be Au.

The metal 23 may include an appropriate weight based on the total weight of the cathode 20 on which the metal 23 is formed. When the content of the metal 23 is excessively small, the potential difference of the cathode 20 cannot be induced. Therefore, the effect of inhibiting lithium dendrite growth due to lithium ion migration is insignificant. When the content of the metal 23 is excessively large, the metal (23) The pores of the cathode 20 are clogged to make it difficult to use one side of the cathode 20, and thus it may not be possible to take advantage of the three-dimensional structure of the cathode having pores.

In the present invention, the porosity of the current collector 10 may be 50 to 90%, preferably 60 to 80%, more preferably 65 to 75%. If the porosity is less than the range, the lithium dendrite growth inhibitory effect is minimal in the lithium secondary battery to which the current collector 10 is applied. If the porosity is greater than the range, the mechanical properties of the current collector 10 may be reduced.

In the present invention, the thickness of the current collector 10 may be 20 to 200 μm, preferably 50 to 150 μm, more preferably 80 to 120 μm. If the thickness of the current collector 10 is less than the above range, the durability of the current collector 10 may be reduced, and if the current collector 10 is more than the above range, the battery may be thickened.

In the present invention, the current collector 10 may be made of an electrically conductive metal, the electrically conductive metal is one selected from the group consisting of Al, Cu, Au, Ag, In, Mg, Ni and alloys thereof. It may be abnormal. Depending on the redox potential of the metal can be used as a positive electrode current collector or a negative electrode current collector. Preferably, the current collector 10 may be made of Cu.

Manufacturing method of current collector

The present invention also relates to a method for manufacturing a current collector comprising the step of forming a metal on one surface of the three-dimensional structure current collector.

The metal may be formed on one surface of the current collector by evaporation, and specifically, thermal evaporation, e-beam evaporation, chemical vapor deposition, and physical weather. It may be formed by a deposition method selected from the group consisting of a deposition (PVD) method.

electrode

The invention also relates to an electrode comprising the current collector as described above.

The current collector may be used as a positive electrode current collector or a negative electrode current collector according to the redox potential of the metal included with the binder. For example, if the current collector includes an Al metal, it may be used as a positive electrode current collector, and if the current collector includes Cu metal, it may be used as a negative electrode current collector.

When the current collector according to the present invention is used for a negative electrode of a lithium secondary battery, the negative electrode may be a lithium electrode including lithium metal formed on at least one surface of the negative electrode current collector.

In addition, when the current collector according to the present invention is used for the positive electrode of the lithium secondary battery, the positive electrode may include a positive electrode active material layer formed on at least one surface of the positive electrode current collector. In this case, the positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces thereof. The cathode active material included in the cathode active material layer is LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ , LiNiMnCoO ₂ and LiNi _{1- xy- z} Co _x M1 _y M2 _z O ₂ (M1 and M2 is Independently from each other Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo is any one selected from the group, x, y and z are the atomic fraction of the elements of the oxide composition independently of each other And 0 ≦ x <0.5, 0 ≦ y <0.5, 0 ≦ z <0.5, and x + y + z ≦ 1) or two or more of these slurries.

Lithium secondary battery

The present invention also relates to a lithium secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode includes the current collector as described above, wherein the current collector faces the separator. Metal may be formed on the bottom surface opposite to the upper surface.

2 is a schematic diagram showing a partial structure of a lithium secondary battery according to the present invention.

Referring to FIG. 2, in the lithium secondary battery 100 having a structure in which a separator 40 is interposed between the positive electrode 20 and the negative electrode 30, the negative electrode 30 has a metal 13 on one surface thereof as described above. The formed three-dimensional structure current collector 10 may be included.

The three-dimensional structure current collector 10 includes an upper surface 11 and a lower surface 12 facing the separator 40, and the metal 13 is formed on the lower surface 12 of the upper surface 11 and the lower surface 12. It may be.

Due to this structural feature, since lithium ions move and grow to the metal 13 formed on the lower surface 12 of the three-dimensional structure current collector 10, the growth of lithium dendrites can be suppressed.

In the lithium secondary battery according to the present invention, the positive electrode and the negative electrode are as described above.

The separator may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate commonly used in an electrochemical device. For example, a polyolefin-based porous membrane or a nonwoven fabric may be used. It is not specifically limited.

Examples of the polyolefin-based porous membrane, polyolefin-based polymers, such as polyethylene, polypropylene, polybutylene, polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, respectively, or a mixture thereof One membrane may be mentioned.

The nonwoven fabric may include, for example, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, or polycarbonate. ), Polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide and polyethylenenaphthalene, alone or in combination The nonwoven fabric formed from the polymer which mixed these is mentioned. The structure of the nonwoven can be a spunbond nonwoven or melt blown nonwoven composed of long fibers.

The thickness of the porous substrate is not particularly limited, but may be 1 μm to 100 μm, preferably 3 μm to 50 μm, and more preferably 5 μm to 30 μm. The pore size and pore present in the porous substrate are also not particularly limited, but may be 0.001 μm to 50 μm and 10% to 95%, respectively.

In addition, the electrolyte salt contained in the nonaqueous electrolyte solution which can be used in the present invention is a lithium salt. The lithium salt may be used without limitation as those conventionally used in the lithium secondary battery electrolyte. For example, the lithium salt is LiFSI, LiPF ₆ , LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, may be one or more selected from the group consisting of lithium chloroborane and lithium 4-phenyl borate.

As the organic solvent included in the aforementioned non-aqueous electrolyte, those conventionally used in the lithium secondary battery electrolyte may be used without limitation, and for example, ethers, esters, amides, linear carbonates, and cyclic carbonates may be used alone or in combination of two or more. It can be mixed and used. Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a slurry 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, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and any one selected from the group consisting of halides thereof, or two or more of these slurries. These halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.

In addition, specific examples of the linear carbonate compound may be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate. Two or more of these slurries and the like may be representatively used, but are not limited thereto. In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, have high dielectric constants and can dissociate lithium salts in the electrolyte more efficiently. By using a low viscosity, low dielectric constant linear carbonate mixed in an appropriate ratio it can be made an electrolyte having a higher electrical conductivity.

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 two or more of these slurries may be used. It is not limited to this.

In addition, the ester in the organic solvent is methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, Any one selected from the group consisting of α-valerolactone and ε-caprolactone or two or more of these slurries may be used, but is not limited thereto.

The injection of the nonaqueous electrolyte may be performed at an appropriate step in the manufacturing process of the electrochemical device, depending on the manufacturing process and the required physical properties of the final product. That is, it may be applied before the electrochemical device assembly or the final step of the electrochemical device assembly.

The lithium secondary battery according to the present invention may be a lamination (stack) and folding process of the separator and the electrode in addition to the winding (winding) which is a general process.

In addition, the shape of the battery case is not particularly limited, and may be in various shapes such as cylindrical, stacked, square, pouch or coin type.

The present invention also provides a battery module including the lithium secondary battery as a unit cell.

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

Examples of the medium-to-large device include a power tool that is driven by an electric motor; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; Electric motorcycles including electric bicycles (E-bikes) and electric scooters (E-scooters); Electric golf carts; Power storage systems and the like, but is not limited thereto.

Hereinafter, preferred examples are provided to help the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and various changes and modifications within the scope and spirit of the present invention are apparent to those skilled in the art. It goes without saying that changes and modifications belong to the appended claims.

Example 1: Preparation of a three-dimensional structure current collector and a half cell in which Au metal is formed on the lower surface

(One) Fabrication of 3D structure current collector with metal formed on one side

Au metal was thermally deposited on one surface of a Cu current collector in the form of a three-dimensional foam.

(2) Electrode manufacturing

The negative electrode was prepared by depositing a lithium metal layer having a thickness of 5 μm on one surface of the three-dimensional structure current collector.

The positive electrode was prepared by adding 96% by weight of LiCoO ₂ , ₂ % by weight of Denka black (conductor) and 2% by weight of PVdF (Polyvinylidene fluoride, binder) to NMP (N-Methyl-2-pyrrolidone) as a positive electrode active material. After that, the positive electrode slurry was coated on one surface of an aluminum current collector to a thickness of 65 μm, dried and rolled, and then punched to a predetermined size to prepare a positive electrode.

(3) Coin-type half battery manufacturing

After interposing the polyolefin separator between the negative electrode and the positive electrode prepared as described above, 1M LiPF ₆ dissolved electrolyte was injected into a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (DEC) were mixed in a volume ratio of 50:50. A coin-type half cell was prepared.

In this case, a surface on which the Au metal was deposited on the three-dimensional structure current collector of the negative electrode was referred to as a lower surface, and when the opposite side of the lower surface was referred to as an upper surface, the coin-type half cell was prepared by placing the upper surface and the separator facing each other.

Example 2: Preparation of a three-dimensional structure current collector and a half cell in which Ag metal is formed on the lower surface

In the same manner as in Example 1, Ag metal was used instead of Au to prepare a three-dimensional structure current collector and a half cell.

Example 3: Fabrication of a three-dimensional structure current collector and a half cell in which Au metal is formed on the lower surface

In the same manner as in Example 1, the amount of Au metal formed on the lower surface of the three-dimensional structure current collector was reduced to prepare a three-dimensional structure current collector and a half cell.

Example 4: Preparation of a three-dimensional structure current collector and a half cell in which Au metal is formed on the lower surface

In the same manner as in Example 1, the amount of Au metal formed on the lower surface of the three-dimensional structure current collector was increased to prepare a three-dimensional structure current collector and a half cell.

Comparative Example 1: 2-D Structure Cu Current Collector and Half-Cell Fabricated Using Same

In the same manner as in Example 1, a half cell was manufactured using a Cu foil as a two-dimensional structured current collector instead of a three-dimensional structured current collector on which metal was formed.

Comparative example  2: two-dimensional Cu formed with Au metal House  And manufacturing a half cell using the same

In the same manner as in Example 1, Ag metal was formed in the two-dimensional structure current collector instead of the three-dimensional structure current collector, and then a half battery was manufactured using the same.

Comparative example  3: Au metal  Unformed 3-D Structure House  And manufacturing a half cell using the same

A half cell was manufactured in the same manner as in Example 1, but without forming a metal in a Cu current collector having a three-dimensional foam.

Comparative example  4: 3D structure with Au metal on both sides House  And manufacturing a half cell using the same

The same procedure as in Example 1 was performed except that Au metals were formed on both surfaces of the Cu current collector in the form of a three-dimensional foam, that is, both the upper and lower surfaces thereof, to prepare a half battery.

Comparative example  5: 3D structure with Au metal House  And manufacturing a half cell using the same

A battery was prepared in the same manner as in Example 1 except that Au metal was formed on an upper surface of a Cu current collector having a three-dimensional foam.

Although the present invention has been described above by means of limited embodiments and drawings, the present invention is not limited thereto. Various modifications and variations are possible without departing from the scope of the appended claims.

10: whole house
11: top 12: bottom
13: metal
20: anode 30: cathode
31: negative electrode active material layer
40: separator
100: lithium secondary battery

Claims (10)

A current collector having a three-dimensional structure, the metal is formed on one surface. The method of claim 1,
The metal collector is a metal particle. The method of claim 1,
The metal current collector is at least one member selected from the group consisting of Au, Zn, Mg, Ag, Al, Pt, Si, Ca and alloys thereof. The method of claim 1,
The metal is the current collector is deposited on one surface of the current collector. The method of claim 1,
The current collector includes a top surface facing the separator and a bottom surface opposite to the top surface,
The metal is the current collector is formed on the lower surface. The method of claim 1,
The current collector is one, at least one member selected from the group consisting of Al, Cu, Zn, Au, Ag, In, Mg, Ni and alloys thereof. The method of claim 1,
Porosity of the current collector is 50 to 90%, the current collector. The method of claim 1,
The collector has a thickness of 20 to 200 μm. An electrode comprising the current collector of any one of claims 1 to 8. In a lithium secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode,
The negative electrode includes the current collector of any one of claims 1 to 8,
The current collector is a lithium secondary battery, a metal is formed on the lower surface located opposite to the upper surface facing the separator.

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