KR20090104991A - The manufacturing method of monolith electrode for li-ion battery and the monolith electrode manufactured by the same - Google Patents

Abstract

PURPOSE: A method for manufacturing monolith electrode for Li-ion battery is provided to innovatively increase the portion of active materials which mainly participates in chemical reaction of a battery. CONSTITUTION: A method for manufacturing monolith electrode for Li-ion battery comprises the steps of: preparing a mixture of a slurry form by rotating current collector metal powder and active material powder; completely drying the mixture at 40~150°C in a heat-resistant glass; pulverizing the dried mixture, pouring it in a mold, and applying the pressure of 50~500kg/cm^2 to mold a disc type specimen; heating the molded specimen at 300~1000°C in nitrogen or hydrogen gas atmosphere; and forming an electrode by current collector metal together with active material.

Description

TECHNICAL FIELD OF THE INVENTION An integrated electrode manufacturing method for a lithium ion battery, and an integrated electrode manufactured by the method TECHNICAL FIELD

The present invention relates to an electrode for a lithium ion battery, and more particularly to an electrode having a capacity and stability suitable for large lithium ion batteries, and a method for producing the electrode.

In general, a material currently used as an active material in a lithium ion battery is graphite and has a capacity of 372 mAh / g. However, due to the development of the technology industry, the capacity of the battery is required to be improved, and research on high capacity materials that can replace graphite is being actively conducted. Among the materials under study, representative materials are oxides. However, although the capacity of the oxide is more than 600 mAh / g is much higher than the graphite, it has been pointed out that the problem of the volume change of the oxide generated during the charge / discharge.

The problem caused by the volume change of the oxide is caused by the structure of the electrode currently being used. Currently, electrodes for lithium ion batteries form an electrode by coating electrode materials on a current collector in the form of a metal foil that moves and supplies electrons. The electrode material is an active material that mainly reacts with lithium ions to generate electrical energy, a binder for fixing the current collector and the material, and a conductor that improves the conductivity of the active material to facilitate electron transfer to the active material. It is a mixture composed of conductors. In the actual cell, a current collector, a binder, and a conductor participate in the chemical reaction that converts chemical energy into electrical energy. Therefore, this component is essential for driving the battery in the conventional electrode, but when viewed only the overall cell reaction, it acts as a factor for reducing the specific capacity per unit volume, per weight.

On the other hand, such a structure may not be a problem when using commercially available graphite as an active material. However, when an oxide having a higher capacity than graphite is used as the active material, the active material is separated from the current collector due to the volume change of the active material generated during charging / discharging. Since the separation of the current collector and the active material causes the deterioration of the charge / discharge cycle characteristics, many researchers have continuously studied to solve this problem.

Most of the researches to solve the problem of separating the current collector and the active material are concentrated on the method of processing the active material while maintaining the current electrode structure. A typical example is a method of forming a composite with materials that can simultaneously provide electrical and ionic conductivity, such as carbon materials. However, the current electrode structure is a structure that can not completely avoid the separation of the current collector and the active material as long as the active material is volume expansion and contraction, such a study can not be a fundamental solution.

In addition, the current electrode structure is very thin (tens of tens to hundreds of μm), which makes it a bit difficult to build a large battery. Therefore, in order to develop a large lithium ion battery for use in a field such as a hybrid vehicle, it is very urgent to develop a new electrode structure.

In order to solve the above problems, the present invention has been made to provide a new electrode structure developed to facilitate the application to large lithium ion batteries by improving the capacity by using a structure that is easy to control the ratio of oxide as its basic purpose. .

Another object of the present invention is to provide a method for producing an electrode of a lithium ion battery that withstands volume change of an active material and exhibits stable charge / discharge cycle characteristics, and an electrode manufactured by the method.

That is, the technical problem of the present invention is developed by the development of a new concept electrode structure which is advantageous for application to large batteries requiring high output and high capacity, well resisting the volume change of the active material, and improving the capacity by increasing the ratio of oxide. You can summarize.

On the other hand, other unspecified objects of the present invention will be further considered within the range that can be easily inferred from the following detailed description and effects.

In order to achieve the above object, the present invention is characterized in that in the bulk form by mixing them integrally, unlike the conventional negative electrode that the current collector metal and the active material is separated into an independent layer. That is, the present invention is a negative electrode for a lithium ion battery,

The current collector metal and the active material are mixed together without being divided into independent layers,

The current collector metal molecules adhere to the surface of the active material molecules, and the current collector metal and the active material are integrally formed.

In addition, the powder of the current collector metal and the active material powder having a particle size larger than that of the current collector metal powder are mixed to form a mixed powder, and it is preferable to form an integrated electrode by molding the powder through heat treatment.

Moreover, the manufacturing method of the negative electrode for lithium ion batteries of this invention,

(1) rotating the mixed powder of the current collector metal powder and the active material powder to form a mixture in the form of a slurry;

(2) immersing the mixture in a heat resistant glass and completely drying at a temperature in the range of 40 to 150 ° C;

(3) pulverizing the dried mixture into a mold and applying a pressure in the range of 50 to 500 kg / cm 2 to form a disk-shaped specimen; And

(4) heat-treating the molded specimen at a temperature in the range of 300 to 1000 ° C. in a nitrogen gas atmosphere, and collecting the collector metal and the active material on the surface of the active material molecule by mixing them integrally without being divided into independent layers. All metal molecules are attached, and the current collector metal and the active material form an electrode integrally.

In addition, preferably, the size of the powder of the current collector metal is smaller than the size of the active material powder.

Preferably, the current collector metal is copper, and the active material is metal oxide.

More preferably, the metal oxide may be selected from transition metal oxides including cobalt oxide, nickel oxide, copper oxide, iron oxide, and manganese oxide.

According to the present invention as described above, by directly bonding the active material and the current collector, the current collector not only acts as a binder and a conductor at the same time, but also significantly increases the specific gravity of the active material mainly participating in the chemical reaction of the battery, compared to the existing battery. There is an advantage that can significantly increase the overall unit capacity of the battery.

In addition, the advantage of the electrode structure of the present invention is that the metal oxide has shown the possibility to replace the graphite used as a conventional negative electrode active material. Metal oxides tend to decrease rapidly as unit capacity does not remain constant as charge and discharge proceed due to large volume expansion and contraction and low electrical conductivity. As a result, despite the high reactivity per unit weight to lithium ions compared to the graphite-based negative electrode active material it could not be commercialized. However, according to the present invention, the metal current collector and the metal oxide active material may be directly in contact with each other to have a resistance to volume change, and serve to increase electrical conductivity, thereby maintaining a relatively high unit capacity as charging and discharging proceeds. .

That is, the integrated electrode of the present invention exhibits stable cycle characteristics as a new electrode having a new structure most suitable for using a high capacity oxide as an active material in a lithium ion battery. In addition, the ratio of oxides in the electrodes can be dramatically increased, which is an excellent invention in terms of capacity. Therefore, there is a technically superior effect to prepare a transition period in the lithium theory battery market, which currently occupies most of the battery market.

Furthermore, since the integrated electrode of the present invention is bulk in shape, it is well suited for large battery applications. This will lay the foundation for lithium-ion batteries to be at the center of new large battery markets such as hybrid cars of the future.

 Although effects not specifically mentioned in the specification of the present invention, it is added that the potential effects expected by the technical features of the present invention are treated as described in the specification of the present invention.

Hereinafter, with reference to the accompanying drawings will be described specific details for the practice of the invention. In the following description of the present invention, when it is determined that the subject matter of the present invention may be unnecessarily obscured as matters obvious to those skilled in the art, such as related well-known functions, the detailed description thereof will be omitted.

As shown in FIG. 1, the negative electrode of the lithium ion battery according to the present invention was formed as a bulk integrated electrode by directly mixing or complexing a copper powder as a current collector and an oxide as an active material. For convenience, components other than the negative electrode are omitted. Such a concept of 'integration' means 'junction' of copper and oxide in a molecular size unit as shown in FIG. 1, wherein the chemical reaction of copper and oxide is not considered but only physical bonding. As a mixed powder forming method, a method of mixing using a ball milling method and molding through heat treatment will be described in detail below. However, the composite may be formed by applying heat treatment, chemical reaction, or mechanical energy by attaching an oxide to the surface of a copper molecule unit or by attaching a copper molecule to the surface of an oxide, which is used as a method of mixing two materials such as known sterling. It is noted that a method of forming may also be used.

In order to improve the capacity of a lithium ion battery, it is necessary to raise the ratio of an oxide active material. For this purpose, among the mixed powders of copper and oxide, the copper powder is the smallest possible size, and the oxide powder can be mixed with the largest sized powder within the range that does not harm the charge / discharge capacity characteristics. have. As shown in FIG. 1, the size of the copper powder is made smaller than that of the oxide powder, and the amount of oxide is increased while the amount of copper is lowered by forming a structure surrounding the oxide. In other words, if the particle size of the copper powder of several to several hundred nm level and the oxide of several μm is selected, the weight of the oxide can be made up to about 90% of the total weight due to the difference in the surface area. As such, minimizing the amount of copper used as the current collector improves the performance of the battery per unit weight and volume. Oxides have low electrical conductivity, but as copper wraps around the oxides, it is expected to improve the performance as an electrode by forming a passage through which electrons flow. Such direct attachment can increase the volume of oxides that occur when charging / discharging proceeds. It was studied as a factor to minimize separation from the current collector due to shrinkage. As shown in FIG. 1, it can be seen that according to the microstructure and component distribution of the integrated electrode in which the copper powder and the oxide powder are mixed, the oxide is in direct contact with the current collector metal and uniformly distributed. Meanwhile, for the convenience of molding, a binder may additionally be added, which is subsequently removed by heat treatment.

The oxide usable as the active material may be selected from transition metal oxides such as cobalt oxide, nickel oxide, copper oxide, iron oxide, and manganese oxide.

Selected powders are placed in a nylon jar containing a zirconia ball with a liquid (solvent) evaporating at low temperatures (below 150 ° C) and having a low viscosity (water or alcohol) and rotating (ball- milling) The two powders are mixed to form a mixed slurry. The mixing time is preferably 10 minutes to 72 hours, more preferably 24 hours or more to maintain the mixing time.

A slurry mixture of two powders and a solvent mixed by a ball milling process is placed in a heat-resistant glass container and dried in an oven at a temperature range of about 40 to 150 ° C. Heat-resistant glass containers should be chosen as containers made of materials that are not reactive with both powders. The dried hard powder is produced as a fine powder by using a mortar, etc., and then put in a mold of a desired shape (size range of several mm to several m) and selected according to the pressure (50 ~ 500㎏ / ㎠, depending on the type of powder). ) To form. Large specimens can be molded using cold isostatic presses (CIP).

The molded specimens were annealed using an electric furnace to provide nitrogen gas (N _2). gas) or hydrogen gas (H ₂ gas) is completed by heat treatment for 10 minutes to 10 hours in the temperature range of 300 ~ 1000 ℃ depending on the particle size of copper. The temperature range in the heat treatment process is in the lower temperature range with smaller copper particle size. The slower the temperature during the heat treatment, the longer the heat treatment improves the bonding between the copper and the oxide.

Example

As an example, the copper powder and the cobalt oxide (CoO) powder were selected among the methods using the mixture, mixed using the ball milling method described above, and molded through heat treatment.

In order to produce a specimen having a high CoO ratio, copper powder was prepared as a relatively small powder (purity> 99.9%) of about 300 nm size, and CoO powder was prepared as a relatively large powder (purity> 99%) of about 1 μm size. Selected powders were quantified in a weight ratio of about 40% CoO composition. The two powders quantified were put together with ethanol in a nylon jar containing each zirconia ball, rotated for about 24 hours, and mixed.

The mixed slurry form mixture was placed in a heat resistant glass pyrex dish and completely dried in an oven at a temperature of about 80 ° C., and then the dried mixture was made into fine powder using a mortar. The powder was put into a cylindrical mold having a diameter of 10 mm, and a pressure of 100 kg / cm 2 was formed into a disk-shaped specimen.

The molded specimen was heat treated at 500 ° C. for 2 hours in consideration of the particle size of copper in a nitrogen gas atmosphere using an electric furnace to complete the integrated electrode specimen. The finished specimen was a cylindrical disk specimen with a diameter of about 9.5 mm and a thickness of about 250 μm. The microstructure and component distribution of the finished specimens were confirmed by SEM (Scanning Electron Microscope) and EPMA (Electron Probe X-ray Micro Analyzer). As shown in FIG. 2, CoO was relatively uniformly disposed between copper. Could. (The color in the EPMA image is the area where the component is more red, and the area where the component is less blue or black.)

In order to compare the capacitance characteristics of the integrated electrode and the conventional electrode, the theoretical capacity of CoO was calculated and compared with the current commercially available graphite. The calculated integrated electrodes were dataized by calculating when the weight ratio of CoO was more than 20%, and the existing electrodes had a thickness of (active material) / (binder + conductor) in the range of 60 ~ 300㎛ and 7/3 ~ 9 Calculated in the / 1 range. As a result of calculating and comparing, as shown in FIG. 3, it was confirmed that the integrated electrode of the present invention is superior in terms of capacitance as compared with the existing electrode structure.

The upper portion of FIG. 3 compares the capacity per weight of the electrode. It shows the theoretical capacity that can be obtained with respect to the weight of the entire electrode such as a current collector and an active material, a binder and a conductor. The existing structure has a binder and a conductor, which reduces the theoretical capacity to the electrode weight. In addition, it can be seen that CoO reacts with lithium ions to obtain more electric energy than the graphite active material commercialized for the same weight, resulting in higher capacity than conventional batteries. A shows that CoO reacts with lithium ions to obtain more electrical energy than currently commercially available graphite, resulting in higher capacity than conventional batteries. 'A' shows the capacity when used as an active material by using the currently commercially available graphite as a negative electrode active material. 'B' shows the capacity in the case of manufacturing a conventional electrode structure using CoO. 'C' is a case in which the structure developed in the embodiment of the present invention using CoO is produced, the theoretical range per unit weight increases as CoO increases or decreases in the developed structure.

The lower part of Figure 3 compares the capacity per weight of the active material. Considering the weight of the active material alone, the theoretical capacity is determined by the material regardless of the electrode structure, since the theoretical capacity is inherent to the material reacting with lithium. Commercially available graphite is reported to have about 375 mAh / g, and CoO is known to be about 715 mAh / g.

Charge / discharge cycle characteristics were measured using the integrated electrode specimens completed in the same manner as in the above example.

In order to measure the charge / discharge cycle characteristics, a coin cell (size 2016) was manufactured using the fabricated integral electrode (9.5 mm in diameter, a circular disk having a thickness of 250 μm, and 40% CoO). Separator used Celgard # 2400, and the electrolyte was used LiPF ₆ EC / DEC (1/1 by volume). The coin cell manufactured is in the form of a half cell. After completing the coin cell for 12 hours in an argon glove box (leave it in air), the charge / discharge cycle characteristics in the range of 0.001 to 3.000V are measured using multi-channel battery cycler ™ (Toyo System Co., Ltd) Was measured at 0.2C rate.

As a result, as shown in FIG. 4, it shows about 600 mAh / g, which is somewhat lower than the theoretical capacity of CoO of 715 mAh / g, which is somewhat lower porosity (about 24%, of the electrode manufactured according to the embodiment of the present invention). Existing electrode: about 40 ~ 60%). However, it was confirmed that the cycle characteristics were much more stable than conventional electrodes.

Such stable cycle characteristics can be said to be an advantage caused by directly attaching the active material molecules to the surface of the current collector molecule. The capacity per weight of the electrode including copper is theoretically calculated to be about 286 mAh / g when the ratio of CoO is 40%. As can be seen in FIG. 4, the measured capacity is slightly lower than the calculated value due to the rather low porosity. Measured at mAh / g. However, such a capacity per weight of the electrode is a high capacity almost impossible in the existing structure. In addition, as the amount of CoO is increased, it can be predicted that the charge / discharge capacity per the total weight of the electrode will also increase as the amount of CoO increases, which is calculated as about 429-644 mAh / g at 60-90% of CoO. have.

Therefore, the integrated electrode of the present invention shows a stable cycle characteristics by directly attaching the active material to the current collector, and not only can achieve a dramatic improvement in capacity by increasing the ratio of the active material, but also its bulk shape makes it suitable for large battery applications. It can be said to be a electrode of a new structure.

On the other hand, the scope of protection of the present invention is not limited by the embodiments explicitly described above. In addition, it should be noted that the protection scope of the present invention may not be limited due to obvious changes or substitutions in the technical field to which the present invention belongs.

1 is a cross-sectional view and a schematic view of the microstructure of an integrated electrode according to the present invention.

Figure 2 is a microstructure and component distribution of the integrated electrode produced according to the present invention.

3 is a view comparing the capacitance of the integrated electrode and the conventional electrode according to the present invention.

4 is a view showing the charge and discharge cycle characteristics of the integrated electrode produced according to an embodiment of the present invention.

The accompanying drawings show that they are illustrated as a reference for understanding the technical idea of the present invention, by which the scope of the present invention is not limited.

Claims (8)

In the negative electrode for a lithium ion battery, The current collector metal and the active material are mixed together without being divided into independent layers, An integrated negative electrode for a lithium ion battery, wherein a current collector metal molecule adheres to a surface of an active material molecule so that the current collector metal and the active material are integrally formed. The integrated negative electrode of claim 1, wherein the current collector metal is copper, and the active material is a metal oxide. The integrated negative electrode of claim 2, wherein the metal oxide is selected from transition metal oxides including cobalt oxide, nickel oxide, copper oxide, iron oxide, and manganese oxide. The method according to any one of claims 1 to 4, wherein the powder of the current collector metal and the active material powder having a larger particle size than the current collector metal powder are mixed to form a mixed powder, which is formed by heat treatment. An integrated cathode electrode for a lithium ion battery, characterized by forming an integrated electrode. In the cathode electrode manufacturing method for a lithium ion battery, (1) rotating the mixed powder of the current collector metal powder and the active material powder to form a mixture in the form of a slurry; (2) immersing the mixture in a heat resistant glass and completely drying at a temperature in the range of 40 to 150 ° C; (3) pulverizing the dried mixture into a mold and applying a pressure in the range of 50 to 500 kg / cm 2 to form a disk-shaped specimen; And (4) heat-treating the shaped specimens at a temperature in the range of 300 to 1000 ° C. in a nitrogen or hydrogen gas atmosphere, wherein the current collector metal and the active material are not separated into independent layers and are integrally mixed to thereby form an active material molecule surface. A current collector metal molecule is attached to the current collector metal, and the current collector metal and the active material form an electrode integrally. The method of claim 5, wherein the current collector metal is copper, and the active material is a metal oxide. The method of claim 6, wherein the metal oxide is selected from transition metal oxides including cobalt oxide, nickel oxide, copper oxide, iron oxide, and manganese oxide. The method of claim 4, wherein a size of the powder of the current collector metal is smaller than a size of the active material powder.

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