KR20130069948A - Methods of preparation for anode active materials of lithium secondary batteries and lithium secondary batteries containing the same - Google Patents

Abstract

PURPOSE: A negative electrode active material manufacturing method is provided to improve life characteristics of a battery and to suppress an initial irreversible phenomenon. CONSTITUTION: A negative electrode active material manufacturing method comprises preparing a metal wire from a Si metal or a Si alloy; supplying the wire to a reaction chamber filled with a reaction gas including at least one gas selected from an inert gas, a hydrocarbon gas, and an oxygen gas; and forming a metal nanopowder by pulsed wire evaporating the wire supplied into the reaction chamber. The inert gas is at least one selected from the group consisting of helium, neon, argon, and nitrogen gases.

Description

Method of preparation for anode active materials of lithium secondary batteries and lithium secondary batteries containing the same}

The present invention relates to a negative electrode active material for a lithium secondary battery, and to a method for producing a Si-based negative electrode active material.

Carbon materials such as graphite have been commonly used as a negative electrode material of a lithium secondary battery in which charge and discharge are performed by insertion and desorption of lithium ions. However, as shown in FIG. 1, when the negative electrode material and the lithium ions are adsorbed and desorbed in the charging and discharging process, the carbon material has a problem that the capacity of the carbon material is significantly smaller than that of other metal materials.

That is, metal materials such as Si, Sn, Al, Ag, and the like have a high capacity of 2 to 10 times that of graphite, and in particular, Si is the metal having the highest capacity per volume and mass.

However, when the metal materials are used as the negative electrode, as shown in FIG. 2, a large volume change occurs during adsorption and desorption of lithium ions. As a result, cracks occur as the charge and discharge are repeated, resulting in a collapse of the structure. That is, there is a problem that it is difficult to secure the life characteristics due to the large volume change.

Even for Si-based negative active materials, which are attracting attention as next-generation negative electrode materials for increasing the capacity of lithium secondary batteries, it is difficult to secure lifespan and stability due to volume expansion problems, and various studies are being conducted to solve them. The Si-based negative active material developed so far is as follows:

(1) SiO _x

A sort of buffer for the role of the volume change is believed to be the structure of the form to the Si metal present, the SiO ₂ matrix in the Si SiO ₂ matrix, as shown in Fig. 3 because it is advantageous in improving the life characteristics. However, as the fraction of SiO ₂ is higher, the capacity is lowered, so there is a limitation in increasing the ultra-high capacity, and there is a disadvantage in that the manufacturing cost is high and mass production is difficult. In recent years, research is being conducted to add a metal for promoting the reduction of Si to lower the fraction of SiO ₂ .

(2) Silicon nano composite (hereinafter SNC)

As shown in FIG. 4, as a nanocomposite form of Si metal and carbon, there is no material that does not react with lithium, which is advantageous for high capacity and low manufacturing cost. However, with Si, carbon also has a problem that it is difficult to secure the life characteristics because the volume expansion occurs. In order to solve this problem, research is being conducted to minimize the stress upon volume expansion by producing Si metal in nano size.

(3) Si-alloy

As shown in FIG. 5, alloying with a metal which does not occur adsorption and desorption reaction of Si metal and lithium, is advantageous in improving the life characteristics because the metal that does not react with lithium suppresses the volume change of Si, SiO _x It is advantageous for higher capacity since the metal content can be lower than that of SiO ₂ matrix in the form. However, it is not easy to select an alloy composition with an appropriate combination of solving the initial irreversible phenomenon and excellent life characteristics, and it is difficult to nano-particle metal.

(4) nano Si

As shown in FIG. 6, there are a rod type and a particle type formed by using a binder having a high adhesion force, which are formed in a manner of grain growth through thin film deposition on a substrate. Stabilization of the battery structure through the vertical expansion suppression is advantageous to improve the life characteristics, but has a disadvantage that it is difficult to be applied to the existing battery manufacturing process as it is.

Recent studies on Si-based negative electrode active materials relate to binders and electrolyte compositions for improving nanoparticles or complexation for volume expansion inhibition, surface treatment for initial irreversible inhibition, and adhesion to electrode plates.

The present invention is to provide a method for producing a Si-based negative electrode active material that can improve the life characteristics of the battery and suppress the initial irreversible phenomenon and a lithium secondary battery prepared therefrom.

The present invention comprises the steps of preparing a metal wire from Si metal or Si alloy; Supplying the wire into a reaction chamber filled with a reaction gas comprising at least one gas selected from an inert gas, a hydrocarbon gas and an oxygen gas; And forming a metal nanopowder by instantaneously vaporizing a metal wire supplied into the reaction chamber (Pulsed Wire Evaporation: PWE).

Preferably, in the manufacturing of the metal wire, a metal wire is manufactured by melting the Si metal and then injecting it into an elongated mold to cool the metal wire or by cutting the Si wafer.

Preferably, in the manufacturing of the metal wire, at least one metal selected from the group consisting of Si, Sn, Ge, Al, Ti, and Cu is melted, and then, the metal wire is manufactured through a drawing process.

Preferably, in the manufacturing of the metal wire, the metal wire is manufactured by melting one or more metals selected from the group consisting of Si, Sn, Ge, Al, Ti, and Cu, and injecting the same into a mold to cool the metal wire. .

Preferably, the inert gas is one or more selected from the group consisting of helium, neon, argon and nitrogen gas.

Preferably, the hydrocarbon gas is one or more selected from the group consisting of methane, ethane, ethylene, propane, propylene, butane and butylene.

Preferably, the oxygen gas is O ₂ or purified air.

Preferably, the reaction gas includes 1 to 80% by volume hydrocarbon gas of the total reaction gas.

Preferably, the reaction gas contains 1 to 80% by volume of oxygen gas of the total reaction gas.

Preferably, the instantaneous vaporization in the step of forming the metal nano powder is made by a pulse voltage of 10 to 50kV applied in a period of 0.5 to 10 seconds.

The present invention provides a lithium secondary battery comprising a Si-based negative electrode active material prepared by the above method.

According to the present invention, as the charge / discharge reaction proceeds in the negative electrode active material, it is possible to solve the problem of deterioration of the life characteristics of the battery due to volume expansion. In addition, through the composition control on the surface of the active material particles it is possible to solve the problem of the initial irreversible phenomenon and thereby the battery capacity is reduced.

1 is a theoretical capacity per unit volume and per mass for adsorption and desorption reactions of lithium ions with lithium ions.
Figure 2 is a picture of the structural change of the surface of the metal material appearing due to the adsorption and desorption of lithium ions due to charging and discharging, and illustrates the internal structure change.
3 is a Si-based negative active material structure of the SiO _x form.
4 is a Si-based negative active material structure of the SNC form.
FIG. 5 is a schematic diagram of changes in manufacturing and charging and discharging of a Si-based negative active material in a Si-alloy form.
6 is a structure of a Si-based negative electrode active material in the form of nano Si.
7 is a schematic diagram of the PWE process of the present invention.
8 is a photograph of the Si nanoparticles prepared in Example 1.
9 is a photograph of Si-copper alloy nanoparticles including the carbon coaching layer prepared in Example 4.
FIG. 10 is a photograph of Si-copper alloy nanoparticles including the carbon coating layer prepared in Example 5. FIG.

The present invention provides a method for producing a negative electrode active material using a technique of powdering Si metal (hereinafter referred to as "PWE method") by vaporizing with instantaneous electrical energy, and a lithium secondary battery comprising the same.

The PWE method utilizes a phenomenon in which a high density current passes through a metal wire and explodes in the form of fine particles or vapor. As shown in FIG. 7, when a high voltage is applied to the metal wire located between the two electrodes, the current passing through the wire is increased up to 10,000 to 50,000 mA to induce resistance heating of the wire. The wire is rapidly heated and melted by the resistance heating, and as the temperature rises continuously, the surface of the metal wire is cooled by the surrounding medium, while the inside of the metal wire forms droplets and vaporizes as discharge between the droplets. . The vaporized metal gas is confined inside the metal wire, and when the pressure inside the wire reaches a threshold or more, it instantly expands and then explodes to expel the metal nanoparticles at high speed.

Specifically, the present invention comprises the steps of preparing a metal wire from Si metal or Si alloy; Supplying the wire into a reaction chamber filled with a reaction gas comprising at least one gas selected from an inert gas, a hydrocarbon gas and an oxygen gas; And forming a metal nanopowder by instantaneously vaporizing the metal wire supplied into the reaction chamber (Pulsed Wire Evaporation (PWE)).

In the manufacturing of the metal wire, a method of cutting a Si wafer into a wire form (for example, 0.2 mm in width and 80 mm in length) may be used. This is because, unlike the conductive metals, Si is not ductile, and therefore, it is difficult to manufacture Si wires by a normal drawing process. Therefore, in the present invention, a method of cutting a raw material is preferably used to produce a wire using only Si metal. Alternatively, the Si metal wire may be manufactured by melting the Si metal and injecting the same into an elongated mold to cool the Si metal wire.

On the other hand, in the case of mixing and alloying another metal having ductility with Si metal, a conventional drawing process can be used. That is, after melting the Sn, Ge, Al, Ti or Cu with Si can be prepared wire by a drawing process. Here, the wire drawing process means that the molten metal can be manufactured into a rod of about 10 mm through casting, so that the manufactured rod is made thinner while passing the manufactured rod through a die having a smaller hole size. do. Alternatively, the Si alloy melt may be injected into a mold in the form of a wire to be cooled and manufactured. The method of producing the wire of the Si alloy depends on the type and content of the metal to be alloyed. For example, when 90% by weight of Cu and 10% by weight of Si are mixed and melted, a wire is produced through a drawing process, and when 10% by weight of Cu and 90% by weight of Si are mixed and melted, poured into a mold in the form of a wire and cooled. To prepare.

In the present invention for the PWE method, in one embodiment the wire is supplied into a reaction chamber filled with a reaction gas comprising at least one gas selected from an inert gas, a hydrocarbon gas and an oxygen gas. In the reaction chamber, two electrodes are provided for instantaneous vaporization of the metal wire, and preferably, a pulse generator for applying a high voltage is connected to the two electrodes. By the pulse generator, a voltage of 10 to 50 kV may be supplied in a pulse form at a period of 0.5 to 10 seconds. At this time, the supply time of the voltage is preferably instantaneously supplied for a short time of about 10 ^-6 seconds.

In the reaction chamber, a reaction gas including at least one gas selected from an inert gas, a hydrocarbon gas, and an oxygen gas may be supplied.

The inert gas may be gas ions by electrical energy applied to two electrodes in the reaction chamber for instant vaporization. The gas ions condense metal gas and serve to reduce the particle diameter of the metal nanoparticles. As said inert gas, helium, neon, argon, and nitrogen gas can be used individually or in mixture of 2 or more types. Instantaneous vaporization of Si metal or Si alloy wire under such an inert gas environment results in the formation of pure metal nanoparticles.

Next, in order to control the surface state of the metal nanoparticles manufactured, a hydrocarbon gas or an oxygen gas is mixed with the reaction gas supplied into the reaction chamber.

The hydrocarbon gas may be decomposed into carbon atoms by the electrical energy applied to the two electrodes for instant vaporization, and react with the vaporized metal gas to coat the surface of the metal nanoparticles. Since the carbon layer formed on the surface of the metal nanoparticles blocks particle growth due to aggregation or external thermal energy between the particles, metal nanoparticles having a relatively small size can be manufactured as compared with the metal nanoparticles prepared under an inert gas environment.

The hydrocarbon gas may be one or more selected from the group consisting of methane, ethane, ethylene, propane, propylene, butane and butylene.

The thickness of the carbon coating layer may be adjusted according to the content of the hydrocarbon gas. The content of the hydrocarbon gas included in the reaction gas is preferably 1 to 80% by volume of the total reaction gas. If the hydrocarbon gas content is less than 1% by volume, the coating of the carbon layer on the surface of the metal nanoparticles is not made as much as the desired thickness, and if it exceeds 80% by volume, the content of the inert gas is low so that the condensation of the metal gas cannot be sufficiently achieved.

On the other hand, when instantaneous vaporization occurs under a reaction gas containing oxygen gas in the production of metal nanoparticles, it is possible to form an oxygen coating layer, that is, an oxide layer on the surface of the metal nanoparticles to be produced. Oxygen gas is pure O ₂ Gas can be used and optionally purged air containing oxygen. In addition, the thickness of the oxide layer may be adjusted according to the mixing ratio of the oxygen gas included in the reaction gas. In the present invention, preferably 1 to 80% by volume of the oxygen gas of the total reaction gas is mixed with the reaction gas. If the oxygen gas content is less than 1% by volume, the oxide layer coating on the surface of the metal nanoparticles is not made as much as the desired thickness, and if it exceeds 80% by volume, the content of the inert gas is low and the condensation of the metal gas cannot be sufficiently achieved.

According to the present invention, the Si-based negative electrode active material in the form of nanoparticles can be prepared, and at the same time, by controlling the type and content of the hydrocarbon gas or oxygen gas mixed in the reaction gas, the surface of the carbon coating layer or the oxide layer and the thickness thereof are controlled. The composition can be controlled. Therefore, when the nanoparticles of Si metal or Si alloy prepared as described above are used as a negative electrode active material for a lithium secondary battery, the initial irreversible reaction is suppressed and the volume expansion due to the charge / discharge reaction is suppressed. Efficiency and lifespan characteristics can be improved.

The present invention forms an active material layer including the prepared negative electrode active material on the current collector to provide a negative electrode for a lithium secondary battery. As the current collector, one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

The active material layer also contains a binder and optionally a conductive material together with the negative electrode active material. The binder may be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, carboxylated polyvinylchloride, polyvinyldifluoride, polymer including ethylene oxide, polyvinylpyrroly Don, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon and the like can be used, but is not limited thereto. .

As the conductive material, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder such as copper, nickel, aluminum, silver, or metal fiber may be used. Of conductive materials can be mixed and used. The negative electrode having the above-described configuration may be prepared by mixing a negative electrode active material, optionally a conductive material and a binder in a solvent such as N-methylpyrrolidone to prepare a composition for forming a negative electrode active material layer and then applying the composition to a current collector. Can be.

The negative electrode having the above structure can be applied to a lithium secondary battery. The lithium secondary battery includes a cathode including a cathode, a cathode active material capable of intercalating and deintercalating lithium ions, and an electrolyte including a non-aqueous organic solvent and a lithium salt.

The invention will be described through the following examples. However, this is for the purpose of facilitating the understanding of the invention and the invention should not be regarded as being limited thereto.

Example  One

Si nanoparticles were prepared using the PWE method.

The PWE method was prepared by instantaneously discharging a high voltage and a large current charged in a capacitor to a metal wire using pulse power. As the metal wire, a Si wafer (Wafer Korea Co., Ltd., 200 mm) was cut at intervals of 0.2 mm in width and manufactured in a bar shape having a length of 100 to 200 mm. Si nanoparticles were prepared by applying a pulse voltage of 25 kV for 10 ⁻⁶ seconds under a reaction gas atmosphere of 1.5 bar of argon.

Si nanoparticles prepared by scanning electron microscopy were photographed (FIG. 8).

Example  2

Si nanoparticles including a carbon coating layer were prepared in the same manner as in Example 1 except that the reaction gas was used as the argon / methane gas (80/20% by volume) in Example 1.

Example  3

Si nanoparticles including an oxide layer were manufactured in the same manner as in Example 1 except that the reaction gas was used as the argon / O ₂ gas (80/ ₂₀ % by volume) in Example 1.

Example  4

After mixing 90% by weight of Cu and 10% by weight of Si to melt at a high temperature, casting a rod of 10 mm and then drawing a 0.2 mm diameter Si-copper (1: 9) alloy wire through a drawing process.

Si-copper nanoparticles including a carbon coating layer were prepared in the same manner as in Example 2, except for using the prepared Si-copper (1: 9) alloy wire. Si-copper nanoparticles prepared by scanning electron microscopy were photographed (FIG. 9).

Example  5

After mixing 90% by weight of Si and 10% by weight of Cu to melt at a high temperature, a 200-mm-long Si-copper (9: 1) alloy wire was prepared by pouring into a narrow mold having a diameter of 0.2 mm and quenching.

Si-copper nanoparticles including a carbon coating layer were prepared in the same manner as in Example 2 except for using the prepared Si-copper (9: 1) alloy wire. Si-copper nanoparticles prepared by scanning electron microscopy were photographed (FIG. 10).

Comparative example  One

Si nanoparticles were prepared by grinding a 450 um size Si metal (3303 # grade, Korea Silicon Metal Co., Ltd.) to a size of 100 nm using a beads mill.

Property evaluation

(1) Preparation of Battery Cell

80 wt% of the nanoparticles prepared in Examples 1 to 5 and Comparative Example 1, 10 wt% of Super P, and 10 wt% of polyimide binder were mixed in an N-methylpyrrolidone solvent to prepare a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper foil current collector to prepare a negative electrode.

With the cathode prepared as the working electrode and the metal lithium foil as the counter electrode, a separator made of a porous polypropylene film is inserted between the working electrode and the counter electrode, and propylene carbonate (PC), diethyl carbonate (DEC) and ethylene are used as electrolytes. Lithium ₆ dissolved in a mixed solvent of carbonate (EC) (volume ratio of PC: DEC: EC = 1: 1: 1) at a concentration of 1 mol / L was used for the 2016 coin type half cell ( half cell).

(2) Evaluation of initial efficiency and lifespan

After the charge and discharge was performed under the conditions of 0.1C ↔ 0.1C (single charge and discharge) between 0.01 and 2.0V for the prepared cells, the initial efficiency was evaluated. In addition, 50 cycles of charging and discharging were carried out under the same conditions as described above, and the discharge capacity during the 50th cycle was measured. The results are shown in Table 1 below.

Initial efficiency (%) Life characteristics (%) Example 1 79 81 Example 2 87 87 Example 3 85 86 Example 4 91 93 Example 5 82 83 Comparative Example 1 63 56

As shown in Table 1, the negative electrode active material including the nanoparticles of Si metal or Si alloy prepared from the PWE method as in Examples 1 to 5 is superior to the negative electrode active material containing Si nanoparticles of Comparative Example 1 Life characteristics and initial efficiency are shown.

(3) cathodic expansion rate evaluation

After one charge of the prepared cell, the cell was disassembled and the thickness change of the negative electrode was measured. The expansion rate of the negative electrode was evaluated by measuring the thickness change rate after the charging with respect to the negative electrode thickness before charging. The results are shown in Table 2 below.

% Expansion Example 1 173 Example 2 142 Example 3 135 Example 4 115 Example 5 165 Comparative Example 1 245

As shown in Table 2, the negative electrode including the nanoparticles of the Si metal or Si alloy prepared in Examples 1 to 5 exhibited a low expansion ratio compared to the negative electrode prepared from the Si nanoparticles of Comparative Example 1 also in the expansion rate.

Claims (11)

Preparing a metal wire from Si metal or Si alloy; Supplying the wire into a reaction chamber filled with a reaction gas comprising at least one gas selected from an inert gas, a hydrocarbon gas and an oxygen gas; And forming a metal nanopowder by instantaneously vaporizing a metal wire supplied into the reaction chamber (Pulsed Wire Evaporation (PWE)). In claim 1,
In the manufacturing of the metal wire, a method of manufacturing a negative electrode active material, characterized in that the metal metal is manufactured by melting the Si metal and injecting it into a mold to cool or cutting the Si wafer. In claim 1,
In the manufacturing of the metal wire, a method of manufacturing a negative electrode active material, characterized in that the melting of at least one metal selected from the group consisting of Si, Sn, Ge, Al, Ti, and Cu, followed by a drawing process, produces a metal wire. . In claim 1,
In the manufacturing of the metal wire, the metal wire is manufactured by melting one or more metals selected from the group consisting of Si, Sn, Ge, Al, Ti, and Cu, and injecting the same into a mold to cool the metal wire. A negative electrode active material manufacturing method. In claim 1,
The inert gas is a method for producing a negative electrode active material, characterized in that at least one selected from the group consisting of helium, neon, argon and nitrogen gas. In claim 1,
The hydrocarbon gas is a method for producing a negative electrode active material, characterized in that at least one selected from the group consisting of methane, ethane, ethylene, propane, propylene, butane and butylene. In claim 1,
The oxygen gas is O ₂ or a method for producing a negative electrode active material, characterized in that the purified air. In claim 1,
The reaction gas is a negative electrode active material manufacturing method, characterized in that containing 1 to 80% by volume of the hydrocarbon gas of the total reaction gas. In claim 1,
The reaction gas is a negative electrode active material manufacturing method, characterized in that containing 1 to 80% by volume of the oxygen gas of the total reaction gas. In claim 1,
In the forming of the metal nano powder, a method of manufacturing a negative active material, characterized in that instantaneous vaporization of the metal wire is performed by a pulse voltage of 10 to 50 kV applied at a period of 0.5 to 10 seconds. A lithium secondary battery comprising a negative electrode active material prepared by the method of any one of claims 1 to 10.

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