KR20010064617A - Lithium secondary battery cathode composition, lithium secondary battery cathode and lithium secondary battery employing the same - Google Patents

Abstract

PURPOSE: A composition of a lithium secondary battery cathode, and a lithium secondary cathode and a lithium secondary battery by using the same are provided which minimize dendrite and phenomena of lithium being separated from the cathode caused by repeating a charging and a discharging process. CONSTITUTION: The composition of a lithium secondary battery cathode comprises 30-70 wt.% of lithium metal particle powder and 70-30 wt.% of a polymer electrolyte. The cathode of the lithium secondary battery is formed by coating the composition containing the lithium metal particle powder and the polymer electrolyte on a current collector. The method for preparing the cathode of the lithium secondary battery comprises steps of: (i) preparing a slurry by mixing the lithium metal particle powder and the polymer electrolyte; (ii) heating the slurry at 110-130 deg.C for 15-25 minutes; and (iii) coating the prepared slurry on the copper foil. The lithium secondary battery comprises the cathode composition of the lithium secondary battery.

Description

Composition of lithium secondary battery negative electrode, lithium secondary battery negative electrode and lithium secondary battery using same {LITHIUM SECONDARY BATTERY CATHODE COMPOSITION, LITHIUM SECONDARY BATTERY CATHODE AND LITHIUM SECONDARY BATTERY EMPLOYING THE SAME}

The present invention relates to a composition of a lithium secondary battery negative electrode, a lithium secondary battery negative electrode and a lithium secondary battery using the same, and more particularly, to minimize the phenomenon of dendrites and lithium falling off the negative electrode generated by repeated charging and discharging process It relates to a composition of a lithium secondary battery negative electrode, a lithium secondary battery negative electrode and a lithium secondary battery using the same.

With the rapid development of the electric, electronic, communication and computer industries, the demand for high performance and high stability secondary batteries has gradually increased, and in particular, the light and small size and precision of precision electric and electronic products have become a key component in this field. Phosphorus secondary batteries are also required to be thinned and downsized.

In response to such demands, one of the most popular batteries in recent years is a lithium secondary battery.

In general, a lithium secondary battery is composed of a positive electrode, an electrolyte, and a negative electrode. These components are selected to meet the various requirements of the secondary battery, such as battery life, charge and discharge capacity, temperature characteristics, stability.

The anodes used in the conventional secondary batteries include lithium composite oxides (LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ ) which form a layered structure that can be intercalated / deintercalated of lithium (Li) ions, and recently, conductive polymers and disulfides. Polymer anodes using (disulfide) compounds are in the spotlight.

As a negative electrode used in a lithium secondary battery, carbon-based materials such as graphite or coke, such as mesocarbon microbead (MCMB), mesophase carbon fiber (MPCF), or Lithium metal is commonly used.

Among them, polymer electrolytes require excellent ionic conductivity, thermal and electrochemical stability, excellent mechanical strength and adhesion to electrodes, and there is no problem of leakage of electrolyte solution. Component.

The electrolyte is composed of an organic solvent, a lithium salt, and a polymer separator.

The organic solvents generally used in the polymer electrolytes currently used or developed include liquid main organic solvents such as ethylene carbonate and propylene carbonate, and liquid crude organic solvents such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

In addition, lithium hexafluorophosphate (LiPF ₆ ), lithium hexafluorophosphate (LiAsF ₆ ), and the like are used as lithium salts, and polyvinylidene difluoride may be used as an electrolyte that can accommodate such lithium salts. PVdF) series, polyacrylonitrile (PAN) series, polyethylene oxide series or copolymers or mixtures thereof are used, and porous polyethylene and polypropylene separators are mainly used.

However, although the carbon anodes used in the prior art show better stability than lithium metal, the capacity is very low compared to lithium metal, and thus there is a limitation in manufacturing a high density lithium secondary battery.

In addition, recently, when the lowest reduction potential (-3.04V vs SHE) is used, the atomic weight (6.94g / a.u.) Is small and is replaced by lithium metal having a high energy density (3.86Ah / g).

As an example of manufacturing a battery using such a lithium metal, a method of manufacturing a battery and an electrode using lithium fine particles is disclosed in Korean Patent No. 111131.

However, when using lithium metal as a negative electrode as described in the above method, there is a problem that lithium ions dissolved in an electrolyte used as a separator during the discharge process cannot be uniformly deposited on the surface of the lithium metal during charge and discharge.

Therefore, as the charge and discharge process is repeated, a dendrite phenomenon occurs in which lithium ions grow in the form of needles on the surface of the lithium metal. Such a tendon phenomenon shortens the charge and discharge cycle of the lithium secondary battery, and It acts as a cause of short circuits.

In addition, deposition of non-uniform lithium ions during charging causes the lithium to fall off the cathode during discharge, resulting in low capacity and low cycle efficiency.

Therefore, lithium secondary batteries using lithium metal foils have various problems such as low lifespan and short circuit between electrodes.

In addition, the molten metal, such as lithium at high temperature, melted, cooled, and pulverized to form an alloy powder, and then melted at a temperature of about 450 ℃ to add a lithium metal molded in a mold, and then cooled to a lithium secondary battery A method of forming a cathode of US Pat. No. 4,632,889 is disclosed in US Pat. No. 4,632,889. However, the method requires a second high temperature process, which causes a complicated manufacturing process and lowers the yield.

Accordingly, an object of the present invention is to provide a lithium secondary battery negative electrode composition, a lithium secondary battery negative electrode and a lithium secondary battery using the same, which can minimize the phenomenon of dendrites generated by repeated charging and discharging and the phenomenon that lithium falls off from the negative electrode To provide.

1 is a schematic cross-sectional view for explaining the structure of a lithium secondary battery negative electrode according to the present invention.

<Description of Symbols for Major Parts of Drawings>

2: current collector 4: lithium metal fine powder

6: conductive agent 8: polymer electrolyte

In order to achieve the above object of the present invention, the present invention provides a composition of a lithium secondary battery negative electrode comprising a lithium metal particulate powder and a polymer electrolyte.

In addition, the present invention provides a negative electrode of a lithium secondary battery formed by applying a composition comprising a lithium metal particulate powder and a polymer electrolyte to a copper foil (Cu Foil) in order to achieve the above object of the present invention.

In addition, to achieve the above objects of the present invention, the present invention comprises the steps of: i) mixing a lithium metal particulate powder and a polymer electrolyte to prepare a slurry, and ii) applying the slurry onto a copper foil. It provides a method for producing a lithium secondary battery negative electrode, characterized in that.

In addition, the present invention provides a lithium secondary battery comprising a composition of a lithium secondary battery negative electrode comprising a lithium metal particulate powder and a polymer electrolyte in order to achieve the above object of the present invention.

According to the present invention, by adding a polymer electrolyte as a binder to the lithium metal particulate powder to form a composition of a lithium secondary battery negative electrode, it is possible to increase the ion conductivity of the electrode to improve the utilization of the electrode.

Therefore, a lithium secondary battery having high capacity and stable discharge characteristics can be manufactured.

Hereinafter, the present invention will be described in detail.

The composition of the lithium secondary battery negative electrode of the present invention includes lithium metal particulate powder and a polymer electrolyte.

At this time, if the content of the lithium metal particulate powder is less than 30% of the total weight of the composition, the capacity of the entire electrode is reduced, and if the content of the polymer electrolyte is less than 30% of the total weight of the composition, There is a problem that the ion conductivity decreases.

Therefore, the content of the lithium metal particulate powder is 30 to 70% by weight, the content of the polymer electrolyte is preferably 70 to 30% by weight.

In addition, the optimum conditions for determining the content of each component will vary depending on the particle size of the lithium fine particles and the ionic conductivity of the polymer electrolyte.

The polymer electrolyte is a polyacrylonitrile-based, polyacrylate-based, polymethacrylate-based, polyethylene oxide-based, polyvinylidene fluoride-based polymers, mixtures thereof and copolymers thereof and lithium salts are dissolved What mixed electrolyte solution in the ratio of 1: 2-10 is used.

Examples of the electrolyte include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and γ-caprolactone (γ-BL). When the ratio of the polymer mixture to the electrolyte is lower than about 1: 2, the ion conductivity is low, so that efficient ion migration is restricted. The ratio between the polymer mixture and the electrolyte is greater than about 1:10. In the high case, there is a disadvantage in that the role as a binder for fixing the lithium fine particles is restricted.

Therefore, the polymer mixture and the electrolyte solution preferably have a ratio of about 1: 2 to 10 by weight.

Examples of the lithium salts include lithium perchlorate (LiCl0 ₄ ), lithium trifluoromethane sulfonate (LiCF ₃ SO ₃ ), boron lithium fluoride (LiBF ₄ ), and lithium hexafluorophosphate (LiPF ₆ ) each having a concentration of 0.2 to ₄ M. ), Lithium salts such as lithium hexafluoride arsenate (LiAsF ₆ ), or mixtures thereof.

When the concentration of the lithium salt is lower than about 0.2M, the ion number in the electrolyte is low and the ion conductivity is low. When the concentration of the lithium salt is higher than 4M, the ion conductivity is high because the viscosity of the electrolyte is high.

In addition, a conductive agent, for example, a conductive polymer, carbon, or a mixture thereof may be added to the composition of the lithium secondary battery negative electrode.

The conductive agent is not necessary when the lithium metal fine particles included in the composition are in good contact with each other. Otherwise, it is preferable to add about 0 to 25% by weight for electron conduction between the lithium powder particles. Do.

Two methods are largely used as a method of manufacturing a negative electrode of a lithium secondary battery by mixing the lithium metal fine particle powder and the polymer electrolyte.

In the first method, the lithium metal particulate powder and the polymer electrolyte are mixed at room temperature, and then heated at a temperature of about 110 to 130 ° C. for about 15 to 25 minutes to prepare a slurry. Cu) coated on the current collector to prepare a negative electrode of a lithium secondary battery.

In the second method, the polymer electrolyte component may be dissolved in the lithium metal particulate powder and the polymer electrolyte, and a slurry may be mixed by adding a highly volatile solvent in a temperature range of about 80 ° C. to about 80 ° C. After the preparation, it is coated on a copper (Cu) current collector using a doctor blade method, and the solvent is evaporated at a temperature of about 60 ° C. at room temperature (about 25 ° C.) to prepare a negative electrode of a lithium secondary battery.

At this time, tetrahydrofuran (THF), acetone, diethyl ether, etc. are used as a solvent used.

The negative electrode of the lithium secondary battery manufactured as described above has a structure as shown in FIG. 1.

That is, the polymer electrolyte 8 binds the lithium metal fine particle powder 4 on the current collector 2 as a binder and has a shape enclosed.

At this time, when the lithium metal fine particle powders 4 are in good contact with each other, the conductive agent 6 is not necessary. Otherwise, as shown in FIG. 1, carbon or conductive materials are used as the conductive agent 6. The polymer is added to serve as a medium for electron conduction between the lithium metal particulate powder 4.

In this case, since the polymer electrolyte 8 component is included in the negative electrode, ions can penetrate into the lithium electrode through the polymer electrolyte 8 and deposit on the surface of the lithium fine particles existing inside the negative electrode. In the case of a general lithium foil, a deposition reaction that is concentrated on a portion in contact with an electrolyte occurs inside a cathode in which the lithium metal particulate powder 4 is distributed, thereby preventing the concentration of the entire current. The giving role will be shown.

In addition, carbon dioxide, hydrofluoric acid, or a small amount of water may be added to form a stable protective film on the surface of the lithium fine particles.

Subsequently, the present invention forms a lithium secondary battery by forming a separator and a positive electrode in accordance with a conventional method for manufacturing a lithium secondary battery on a negative electrode formed from the composition described above.

Hereinafter, the lithium secondary battery negative electrode composition of the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited by these Examples.

Example 1

1 g of lithium metal fine particles powder having a particle size of 20 µm, 0.15 g of Kynar 2801 (manufactured by Atochem) as a polyvinylidene fluoride polymer, and ethylene carbonate (EC) in which 1 M of lithium hexafluorophosphate (LiPF ₆ ) is dissolved 0.75 g of a mixed solution of / dimethyl carbonate (DMC) (weight ratio 2: 1) and 2.2 g of tetrahydrofuran (THF) were mixed at room temperature, thereby preparing a slurry in which the lithium metal particulate powder was uniformly mixed and well dispersed. . The film was deposited to a thickness of 300 μm using a doctor blade method, coated on a copper current collector, and then dried for two hours to evaporate the tetrahydrofuran to prepare an electrode.

Example 2

1 g of lithium metal fine particles powder having a particle size of 50 μm, 0.15 g of Kynar 2801 (manufactured by Atochem) as a polyvinylidene fluoride polymer, and ethylene carbonate (EC) in which 1 M lithium hexafluorophosphate (LiPF ₆ ) is dissolved 0.75 g of a mixed solution of gamma-caprolactone (γ-BL) (weight ratio 1: 1) and 2.2 g of tetrahydrofuran (THF) were mixed at room temperature, uniformly mixed, and the lithium metal fine powder was well dispersed. Slurry was prepared. The film was deposited to a thickness of 300 μm using a doctor blade method, coated on a copper current collector, and then dried for two hours to evaporate the tetrahydrofuran to prepare an electrode.

Example 3

Ethylene carbonate (EC) / propylene carbonate (PC) in which 1 g of lithium metal fine particles having a particle size of 20 μm, 0.15 g of polyacrylonitrile and 1 M of lithium hexafluorophosphate (LiPF ₆ ) are dissolved (weight ratio 2: 1) 1.2 g of a mixed solution was mixed well at room temperature, and then heated at 120 ° C. for 20 minutes to prepare a slurry. The film was formed into a film having a thickness of 200 μm by using a doctor blade method and coated on a copper ex-met (mesh-like copper current collector) to prepare an electrode.

Example 4

Ethylene carbonate (EC) / dimethyl carbonate (DMC) in which 1 g of lithium metal particulate powder having a particle size of 20 µm, 0.15 g of polymethyl methacrylate, and 1 M of lithium hexafluorophosphate (LiPF ₆ ) are dissolved (weight ratio 1: 0.75 g of the mixed solution of 1) and 2.2 g of tetrahydrofuran (THF) were mixed at room temperature to prepare a slurry in which the lithium metal fine particle powder was uniformly mixed and well dispersed. The film was deposited to a thickness of 300 μm using a doctor blade method, coated on a copper foil, and then dried for two hours to evaporate the tetrahydrofuran to prepare an electrode.

Example 5

Ethylene carbonate (EC) / ethylmethyl carbonate (EMC) in which 1 g of lithium metal particulate powder having a particle size of 20 µm, 0.15 g of polymethyl methacrylate, and 1 M of lithium hexafluorophosphate (LiPF ₆ ) are dissolved (weight ratio 1 0.75 g of the mixed solution of 1), 2.2 g of tetrahydrofuran (THF), and 0.5 g of polypyrrole were mixed at room temperature with a conductive agent to prepare a slurry in which the lithium metal fine particle powder was uniformly mixed. The film was deposited to a thickness of 300 μm using a doctor blade method, coated on a copper foil, and the tetrahydrofuran was evaporated at room temperature to prepare an electrode.

Comparative example

1 g of lithium metal particulate powder having a particle size of 20 µm, 0.15 g of Kynar 2801 (manufactured by Atochem) as a polyvinylidene fluoride polymer, and 1.5 g of tetrahydrofuran (THF) were mixed at room temperature and uniformly mixed. A slurry in which the lithium metal fine particle powder was well dispersed was prepared. The film was deposited to a thickness of 300 μm using a doctor blade method, coated on a copper foil, and then dried for two hours to evaporate the tetrahydrofuran to prepare an electrode.

In the case of using a lithium cobalt oxide (LiCoO ₂ ) as a positive electrode and using a PAN polymer electrolyte using the electrode of Examples 1 to 5 and the electrode of Comparative Example, do not add the electrolyte component inside the negative electrode In the case of the comparative example which does not have a capacity of about 30% of the theoretical capacity of the positive electrode, while the electrode was manufactured using the negative electrodes of Examples 1 to 5, that is, when the electrolyte component is not added to the negative electrode about 80 A dose of% is shown.

As described above, according to the present invention, the lithium secondary battery negative electrode is formed by using the composition in which the polymer electrolyte is added to the lithium metal fine particle powder, so that the deposition reaction is performed on the surface of the lithium metal fine particle powder inside the negative electrode. It is possible to reduce the local current density conducted to the cathode during repeated charge and discharge.

Therefore, lithium ions can be uniformly deposited on the surface of the lithium metal during charge and discharge, thereby minimizing the occurrence of dendrites and suppressing short circuits between the electrodes.

In addition, it is possible to improve the electrical conductivity of the battery to improve the physical and chemical stability of the negative electrode and the charge and discharge rate, and because the lithium metal has a large capacity, the material of the negative electrode can be used less, thereby reducing the mass and thickness of the negative electrode Since the density can be improved, and lithium metal fine particle powder is used, productivity can be improved by easily securing safety during the manufacturing process of the lithium secondary battery.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (18)

A composition of a lithium secondary battery negative electrode comprising lithium metal particulate powder and a polymer electrolyte. According to claim 1, wherein the lithium metal particulate powder is 30 to 70% by weight, the polymer electrolyte composition of the lithium secondary battery negative electrode, characterized in that 70 to 30% by weight. The composition of claim 2, wherein the composition further comprises 0 to 25% by weight of a conductive agent. The composition of claim 3, wherein the conductive agent is made of a conductive polymer, carbon, or a mixture thereof. The method of claim 1, wherein the polymer electrolyte is any selected from polyacrylonitrile-based, polyacrylate-based, polymethacrylate-based, polyethylene oxide-based, polyvinylidene fluoride-based polymers, mixtures thereof, and copolymers thereof. A composition of a lithium secondary battery negative electrode, wherein one polymer and an electrolyte in which lithium salt is dissolved are mixed at a ratio of 1: 2 to 10. The method of claim 5, wherein the electrolyte is ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and gamma-caprolactone (γ-BL) The composition of the lithium secondary battery negative electrode, characterized in that at least one solvent selected from the group consisting of. The method of claim 5, wherein the lithium salt is lithium perchlorate (LiCl0 ₄ ), trifluoromethane sulfonate (LiCF ₃ SO ₃ ), boron lithium fluoride (LiBF ₄ ), hexafluorophosphate having a concentration of 0.2 to 4M The lithium secondary battery negative electrode composition, characterized in that at least one lithium salt selected from the group consisting of lithium (LiPF ₆ ), lithium hexafluoride (LiAsF ₆ ). A negative electrode of a lithium secondary battery formed by applying a composition comprising a lithium metal particulate powder and a polymer electrolyte on a current collector. The negative electrode of a lithium secondary battery according to claim 8, wherein the current collector is a copper foil having a plate structure. The negative electrode of a lithium secondary battery according to claim 8, wherein a passivation layer is further formed on the negative electrode. Iii) mixing the lithium metal particulate powder and the polymer electrolyte to prepare a slurry; And Ii) a method of manufacturing a lithium secondary battery negative electrode comprising applying the slurry on a copper foil. 12. The method of claim 11, wherein the lithium metal fine particle powder is 30 to 70% by weight, and the polymer electrolyte is 70 to 30% by weight. The method of claim 11, wherein the step iii) further comprises mixing 0 to 25% by weight of the conductive agent. The method of claim 11, wherein the step iii) further comprises heating at a temperature of 110 to 130 ℃ for 15 to 25 minutes. The method of claim 11, wherein the step (iii) further comprises the step of mixing any one solvent selected from tetrahydrofuran (THF), acetone and diethyl ether (diethyl ether) of the lithium secondary battery negative electrode Manufacturing method. The method of claim 15, wherein the step iii) is carried out at a temperature of 25 ~ 80 ℃. The method of claim 11, wherein the step ii) is performed using a doctor blade method. Lithium secondary battery comprising a composition of the lithium secondary battery negative electrode according to claim 1.