JP2001266851A - Manufacturing method of electrode for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an electrode for lithium secondary battery that has a high charge and discharge capacity and is excellent in charge and discharge cycle characteristics. SOLUTION: The manufacturing method of lithium secondary battery comprises a method of forming a film by supplying the material from gas phase in which a film having an active material to be alloyed with lithium is formed on a current collector made of a metal which is not alloyed with lithium. A film is formed by a temperature under which a mixed layer dispersed with the components of the current collector is formed in the film at the vicinity of the surface interfacing with the current collector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a novel electrode for a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, a lithium secondary battery, which has been actively researched and developed, has a charge / discharge voltage,
Battery characteristics such as charge-discharge cycle life characteristics and storage characteristics are greatly affected. For this reason, the battery characteristics have been improved by improving the active material used for the electrode.

[0003] When lithium metal is used as the negative electrode active material, a battery having a high energy density per weight and per volume can be formed. However, there is a problem that lithium precipitates in a dendrite shape during charging and causes an internal short circuit. Was.

On the other hand, there has been reported a lithium secondary battery using, as an electrode, aluminum, silicon, tin or the like which electrochemically alloys with lithium during charging (So).
lidState Ionics, 113-115, p57 (1998)). Among these, silicon is particularly promising as a battery negative electrode having a large theoretical capacity and a high capacity, and various secondary batteries using this as a negative electrode have been proposed (Japanese Patent Application Laid-Open No. 10-255768).
No.). However, in this type of alloy negative electrode, sufficient cycle characteristics have not been obtained because the alloy itself, which is an electrode active material, is pulverized by charging and discharging and the current collecting characteristics are deteriorated.

[0005]

SUMMARY OF THE INVENTION The present applicant has proposed a method of forming a thin film such as a CVD method or a sputtering method as an electrode for a lithium secondary battery which uses silicon as an electrode active material and exhibits good charge / discharge cycle characteristics. An electrode for a lithium secondary battery in which a microcrystalline silicon thin film or an amorphous silicon thin film is formed on an electric body has been proposed (Japanese Patent Application No. 11-30 / 1990).
No. 1646).

An object of the present invention is to provide an electrode for a lithium secondary battery using such an active material thin film such as a silicon thin film, which has a high charge / discharge capacity and excellent charge / discharge cycle characteristics. It is to provide a method of manufacturing an electrode for use.

[0007]

SUMMARY OF THE INVENTION The present invention uses a method of forming a thin film by supplying a raw material from a gaseous phase, and converting an active material thin film made of an active material that alloys with lithium from a metal that is not alloyed with lithium. A method of manufacturing an electrode for a lithium secondary battery formed on a current collector, wherein the temperature is at a temperature at which a mixed layer formed by diffusion of a current collector component into an active material thin film near an interface with the current collector is formed. It is characterized in that the thin film is formed.

As a method for forming an active material thin film by supplying a raw material from a gas phase, there are a sputtering method, a CVD method, a vapor deposition method, a thermal spraying method and the like. The material used as the active material in the present invention is a material that is alloyed with lithium, and examples thereof include silicon, germanium, tin, lead, zinc, magnesium, sodium, aluminum, gallium, and indium.

Formed as a thin film by the above thin film forming method
Silicon or germanium in terms of ease of use
An active material containing as a main component is preferable. Also high charge and discharge capacity
In terms of quantity, active materials containing silicon as a main component are particularly
preferable. The active material thin film may be an amorphous thin film or
It is preferably a crystalline thin film. Therefore, the active material thin film
In general, amorphous silicon thin film or microcrystalline silicon thin film
It is preferably used. Amorphous silicon thin film
520 cm corresponding to the crystal area in optical analysis ^-1Nearby
This is a thin film with virtually no peaks detected.
Con thin film corresponds to crystalline region in Raman spectroscopy
520cm to do^-1Near peaks and amorphous regions
480cm^-1Both nearby peaks are virtually detected
Thin film. In addition, amorphous germanium thin film, microcrystal
Germanium thin film, amorphous silicon germanium alloy thin film
Films and microcrystalline silicon germanium alloy thin films are also preferred
Can be used.

[0010] The current collector used in the present invention is formed of a metal that does not alloy with lithium. Examples of the metal that does not alloy with lithium include copper and the like.
In the present invention, the active material thin film is formed at a temperature at which a mixed layer formed by diffusion of the current collector component is formed in the active material thin film near the interface between the current collector and the active material thin film. That is, if the temperature at which the active material thin film is formed (thin film formation temperature) increases, the current-collector component easily diffuses into the active material thin film.
In the present invention, the active material thin film is formed at a temperature at which the current collector component is sufficiently diffused and a mixed layer of the current collector component and the active material component is sufficiently formed in the active material thin film.

When the current collector component is diffused into the active material thin film to form a mixed layer, the adhesion between the current collector and the active material thin film is improved. In addition, since the current collector component is a metal component that is not alloyed with lithium, such a current collector component diffuses into the active material thin film, thereby expanding the active material thin film when inserting and extracting lithium. And the shrinkage is relatively small. For this reason, since the stress accompanying the expansion and contraction of the active material thin film is reduced near the interface with the current collector, it is possible to prevent the active material thin film from peeling off from the current collector due to expansion and contraction of the volume. Adhesion between the conductor and the active material thin film can be further improved.

In such a mixed layer, it is known that the concentration of the current collector component is high near the interface with the current collector, and the concentration decreases toward the surface of the active material thin film. Since the concentration is continuously reduced in the mixed layer, it is considered that the current collector component in the mixed layer forms a solid solution with the active material.

When the temperature for forming the thin film is increased, the current collector component excessively diffuses into the thin film, and an intermetallic compound between the current collector component and the active material is easily formed. When such an intermetallic compound is formed, the number of sites acting as the active material for the active material atoms in the compound decreases, and the charge / discharge capacity of the active material thin film decreases. Further, the formation of the intermetallic compound deteriorates the adhesion between the current collector and the active material thin film. Therefore, it is preferable to form the active material thin film on the current collector at a temperature at which the intermetallic compound of the active material and the current collector component is not formed in the mixed layer. As such a temperature, 300
It is preferred that the temperature be less than ° C.

In the present invention, heat treatment may be performed after forming the active material thin film. By performing such a heat treatment, the current collector component can be further diffused into the thin film. Therefore, when the active material thin film is formed, the current collector component cannot be sufficiently diffused into the thin film, and when a mixed layer having a sufficient thickness cannot be formed, such heat treatment can be performed. preferable. As described above, the heat treatment is preferably performed under such a condition that an excessive diffusion of the current collector component does not form an intermetallic compound between the current collector component and the active material. The temperature of such a heat treatment is preferably a temperature of less than 650 ° C, more preferably 400 ° C or less.

In the present invention, copper is particularly preferable as the current collector component diffused into the active material thin film. Since such copper diffuses from the surface of the current collector into the active material thin film, it is preferable that at least the surface of the current collector contains copper as a main component.

In the present invention, when an active material thin film is formed by a sputtering method, the power density applied to the target containing the constituent atoms of the active material is preferably 50 W / cm ² or less, more preferably 6 W / cm 2. ² or less. At this time, power is supplied by DC voltage, RF voltage,
Alternatively, it may be performed using any of the application of pulse voltages.

In the present invention, it is preferable that the active material thin film is formed on the current collector intermittently. By forming the active material thin film intermittently, the temperature at the time of forming the thin film, that is, the maximum temperature reached in forming the thin film can be lowered. Therefore, the active material thin film can be formed under the condition that the intermetallic compound is hardly formed as described above. As a method of forming a thin film intermittently, there is a method in which a current collector is placed on the outer peripheral surface of a drum-shaped holder, and an active material thin film is formed on the current collector while rotating the holder.

Preferred thin film forming conditions in a thin film forming method for forming a thin film by supplying a raw material from a gas phase will be described below. The substrate temperature is preferably lower than 300 ° C. as described above. If the substrate temperature is too high, an intermetallic compound of the active material and the current collector component may be formed.

The film formation rate is 0.01 nm / sec (0.1Å / sec).
/ Sec) or more. If the film formation rate is too low, even at low temperatures, the effects of surface diffusion and rearrangement become remarkable, and the process becomes close to a thermal equilibrium process, so that an intermetallic compound is easily generated.

The atmospheric pressure (degree of vacuum) is 10 ⁻² to 10 ²
About Pa is preferable. When the atmospheric pressure (degree of vacuum) is higher than this range, a thin film in which powdery particles are deposited is easily formed, and the adhesion to the current collector may be deteriorated. On the other hand, when the atmospheric pressure (degree of vacuum) is lower than this range, the film forming rate becomes extremely slow, and the intermetallic compound is easily generated as described above.

When the active material thin film is formed by the sputtering method, the power density applied to the target is preferably 50 W / cm ² or less as described above, and more preferably 6 W / cm ² or less. If the power density applied to the target becomes too high, the influence of radiant heat from the plasma increases, and an intermetallic compound is easily formed.

As the sputtering gas, a gas that does not react with the target material such as silicon is preferable. From such a viewpoint, He, Ne, Ar, Kr,
Inert gases such as Xe and Rn are preferred. Among them, Ar gas which easily generates plasma and has high sputtering efficiency is particularly preferable.

As a target used for sputtering, a single crystal or polycrystal target is preferable, and its purity is preferably 99% or more. this is,
This is because the contamination of the formed active material thin film with impurities is reduced.

The pressure in the chamber before the start of thin film formation is preferably 0.1 Pa or less. This is also because the contamination of the active material thin film with impurities can be reduced.

Before forming the thin film, it is preferable to perform a pretreatment such as plasma irradiation on the current collector as the substrate. Examples of such pretreatment plasma irradiation include Ar plasma irradiation and hydrogen plasma irradiation. By performing such a pretreatment, the surface of the current collector can be cleaned. Since the temperature of the substrate is increased by such pretreatment, it is preferable that the temperature of the substrate does not exceed 300 ° C.

Further, the current collector serving as the substrate is preferably cleaned before forming a thin film in order to clean the surface. As cleaning agents, water, organic solvents, acids, alkalis,
Neutral detergents and combinations thereof are preferably used.

When performing a heat treatment after forming the thin film,
As described above, the heat treatment temperature is preferably lower than 650 ° C, more preferably 400 ° C or lower. When the heat treatment temperature is increased, an intermetallic compound is easily formed as described above.

The formation of the active material thin film on the current collector is as follows.
It is preferable to perform it intermittently. Therefore, the current collector is set on the outer peripheral surface of the drum-shaped holder as described above, and the active material thin film is formed on the current collector while rotating the holder, or the current is collected on the reciprocating holder. It is preferable to attach a body and form an active material thin film intermittently on the current collector. Further, by providing a plurality of targets for forming an active material thin film and allowing the current collector to sequentially pass through a region facing the target, the active material thin film can be formed intermittently. By forming the active material thin film intermittently in this manner, a rise in the temperature of the substrate can be suppressed. The thickness of one thin film formation is preferably 1 μm or less.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in more detail with reference to examples. However, the present invention is not limited to the following examples, and may be appropriately modified within the scope of the invention. It can be implemented by

(Experiment 1) [Preparation of Negative Electrode] A rolled copper foil (thickness: 2) having a roughened surface by depositing copper on the surface by electrolytic method as a current collector.
6 μm), and a silicon thin film was formed on the current collector using a parallel plate RF sputtering apparatus. Only an Ar gas was used as an atmosphere gas for sputtering, and a 99.999% silicon single crystal was used as a target. While adjusting the Ar gas flow rate and the opening of the exhaust valve, under the thin film forming conditions shown in Tables 1 and 2,
The negative electrodes of Examples 1 to 7 and Comparative Examples 1 to 3 were produced. The thickness of the silicon thin film was about 6 μm.

In Examples 1 to 3 and Comparative Examples 1 and 2, a silicon thin film (active material thin film) was formed by changing the substrate temperature and changing the thin film forming temperature (the highest temperature reached).
In Example 4 and Comparative Example 3, after forming the thin film, heat treatment was performed under the conditions shown in Table 2. In Examples 5 to 7, thin films were formed by changing the power density applied to the target.

The silicon thin film thus formed was analyzed by Raman spectroscopy to identify its crystallinity. When the peak near 480 cm ^-1 was substantially recognized and the peak near 520 cm ^-1 was not substantially recognized, it was regarded as "amorphous". In addition, a peak near 480 cm ⁻¹ was not substantially observed,
A substance in which only a peak near 520 cm ^-1 was substantially observed was defined as "polycrystalline".

It should be noted that the silicon thin film has a thickness of 2.5c on the copper foil.
It was formed in a limited area of mx 2.5 cm using a mask. After forming the active material thin film, a negative electrode tab was attached on a region of the copper foil where the silicon thin film was not formed, thereby completing a negative electrode.

[Preparation of Positive Electrode] 90 parts by weight of LiCoO ₂ powder, 5 parts by weight of artificial graphite powder as a conductive material, and 5 parts by weight of N-methylpyrrolidone containing 5 parts by weight of polytetrafluoroethylene as a binder It was mixed with an aqueous solution to obtain a positive electrode mixture slurry. The slurry was applied to an aluminum foil (thickness 18) as a positive electrode current collector by a doctor blade method.
μm), and then dried to form a positive electrode active material layer. A positive electrode tab was attached on the area of the aluminum foil on which the positive electrode active material layer was not applied, to complete a positive electrode.

[Preparation of electrolyte solution] LiPF was added to an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate.
₆ was dissolved at 1 mol / liter to prepare an electrolytic solution, which was used in the production of the following battery.

[Preparation of Battery] FIG. 2 is a perspective view showing the prepared lithium secondary battery. FIG. 3 is a schematic cross-sectional view showing the manufactured lithium secondary battery. As shown in FIG. 3, a positive electrode and a negative electrode are inserted into an exterior body 10 made of an aluminum laminated film. A silicon thin film 12 as a negative electrode active material is provided on the negative electrode current collector 11, and a positive electrode active material layer 14 is provided on the positive electrode current collector 13. Silicon thin film 12 and positive electrode active material layer 14
Are arranged to face each other with the separator 15 interposed therebetween. The above electrolytic solution is injected into the exterior body 10. The end of the exterior body 10 is sealed by welding,
A sealing portion 10a is formed. The negative electrode tab 17 attached to the negative electrode current collector 11 is taken out through the sealing portion 10a. Although not shown in FIG. 3,
Similarly, the positive electrode tab 18 attached to the positive electrode current collector 13 is also taken out through the sealing portion 10a.

[Charge / Discharge Cycle Test] A charge / discharge cycle test was performed on the lithium secondary battery prepared as described above. The charging and discharging conditions were as follows: after charging with a charging current of 9 mA until the charging end capacity reached 9 mAh, a discharging current of 9 mA
Discharge until the discharge end voltage becomes 2.75 V,
As the charge / discharge of the cycle, the discharge capacity and the charge / discharge efficiency at the first cycle, the fifth cycle, and the 20th cycle were obtained for each battery. The results are shown in Tables 1 and 2. The unit sccm of the flow rate in the following table is 0
° C, 1 atm (101.33 kPa) per minute volume flow rate (cm ³ / min), standard cubic centimeter
s per minute.

[0038]

[Table 1]

[0039]

[Table 2]

Examples 1 to 3 and Comparative Examples 1 and 2 shown in Table 1
As is clear from the results, when the thin film formation temperature (maximum temperature reached) is less than 300 ° C., a high discharge capacity and good charge / discharge efficiency are obtained.

As is clear from the results of Example 1 shown in Table 1, Example 4 and Comparative Example 3 shown in Table 2, when the temperature of the heat treatment performed after the formation of the thin film reaches 650 ° C., the crystallinity of the silicon thin film becomes polycrystalline. It can be seen that the discharge capacity and the charge / discharge efficiency decrease. From this, the heat treatment temperature is 6
It is preferably less than 50 ° C., more preferably 4 ° C.
It is understood that the temperature is not higher than 00 ° C.

As is clear from the results of Example 1 shown in Table 1 and Examples 5 to 7 shown in Table 2, when the power density applied to the target at the time of forming the thin film was 4.94 W / cm ² or less. It can be seen that high discharge capacity and good charge / discharge efficiency can be obtained.

Next, the negative electrodes of Examples 1 to 3 and Comparative Examples 1 and 2 formed by changing the substrate temperature and changing the thin film formation temperature (maximum reaching temperature) were subjected to SIMS (secondary ion mass spectrometry). The concentration distribution of the copper element in the depth direction was measured. As the negative electrode, charging and discharging the negative-electrode before the test, O ₂ ⁺ a using the sputtering source a copper element ⁽⁶³ C
The concentration distribution of u ⁺ ) was measured.

4 to 8 show Examples 1 to 3 and Comparative Example 1.
2 shows the concentration distribution of copper in the depth direction of the negative electrode prepared in Examples 2 to 3, the horizontal axis represents the depth (μm), and the vertical axis represents the atomic density (a
toms / cc: atoms / cm ³ ).
4 shows Example 1, FIG. 5 shows Example 2, FIG. 6 shows Example 3, FIG. 7 shows Comparative Example 1, and FIG. 8 shows Comparative Example 2.

In any of FIGS. 4 to 8, there is a region where the copper concentration is almost uniform and relatively low near the surface. In addition, there is a region where the copper concentration increases from the surface of the active material thin film toward the interface with the current collector. Due to the existence of such a region where the copper concentration increases, near the interface between the active material thin film and the current collector, the mixed region of the active material thin film and the copper element is diffused by the copper element from the current collector. It turns out that exists. It is considered that high adhesion between the current collector and the active material thin film is obtained due to the presence of such a mixed region (mixed layer).

An embodiment in which the substrate is formed at a relatively low substrate temperature
In Examples 1 to 3 (FIGS. 4 to 6), the vicinity of the surface of the active material thin film was measured.
The copper concentration beside is 10²⁰atoms / cc (atoms /
cm ^Three) (About 1%). On the other hand, relatively high
Comparative Examples 1 and 2 in which an active material thin film was formed at a substrate temperature (FIGS.
In FIG. 8), the copper concentration near the active material thin film surface is 10%.^{twenty one}a
toms / cc (atoms / cm^Three) (About 10%)
Is on top. For these reasons, higher substrate temperature
When an active material thin film is formed, copper diffuses throughout the active material thin film
As the active material concentration decreases relatively, the discharge capacity decreases.
It is thought to decrease. Also, copper is high in the active material thin film
The presence of such a compound at a concentration causes the cycle characteristics to deteriorate.
it is considered as. This is probably due to the metal
This is considered to be due to the formation of intermetallic compounds.

(Experiment 2) [Preparation of Negative Electrode] A silicon thin film was formed using an RF sputtering apparatus having a rotating holder as shown in FIG. As a current collector,
The same thing as that used in Experiment 1 was used, and a silicon thin film was formed thereon. The current collector is placed on the outer peripheral surface of the rotary holder 1 shown in FIG. 1, and while rotating the rotary holder 1, a high frequency (R)
F) Electric power was supplied to generate Ar plasma 4, and a silicon thin film was formed on the current collector. The rotation speed of the rotary holder 1 is about 10 rpm, and other thin film forming conditions are as follows.
As shown in Table 3. Note that only Ar gas was used as a sputtering gas, and a target similar to that used in Experiment 1 was used. The silicon thin film was formed to have a thickness of about 6 μm.

[Preparation of Battery and Charge / Discharge Cycle Test] Using the same positive electrode as in Experiment 1, a lithium secondary battery was prepared in the same manner as in Experiment 1, and a charge / discharge cycle test was performed in the same manner as in Experiment 1. Table 3 shows the results.

[0049]

[Table 3]

As is clear from the results shown in Table 3, the thin film formation in Example 8 was the same as that in Example 1 except that the other forming conditions were the same and the power density applied to the target was slightly higher. The temperature (the highest temperature reached) is lower than in the first embodiment. This is because the current collector is placed on the rotating holder, and the active material thin film is formed while rotating the rotating holder, so that the silicon thin film is intermittently formed on the current collector. It is considered that the maximum attained temperature was suppressed low. Further, it can be seen that the discharge capacity and the charge / discharge efficiency are slightly better than in Example 1.

(Experiment 3) Using the same parallel plate type sputtering apparatus as in Experiment 1, the power supplied to the target was changed to DC power or pulse power instead of radio frequency (RF) power, and the power density shown in Table 4 was used. Except for the above, a silicon thin film was formed on the current collector in the same manner as in Example 1 of Experiment 1, and a negative electrode was fabricated in the same manner as in Experiment 1.

[Preparation of Battery and Charge / Discharge Cycle Test] Using the same positive electrode as in Experiment 1, a lithium secondary battery was prepared in the same manner as in Experiment 1, and a charge / discharge cycle test was performed in the same manner as in Experiment 1. Table 4 shows the results.

[0053]

[Table 4]

As is evident from the results shown in Table 4, the use of a DC power supply or a pulse power supply instead of the high-frequency power supply lowers the thin film formation temperature (maximum temperature reached) as compared with the first embodiment. You can see that. In addition, the discharge capacity and charge / discharge efficiency of the obtained lithium secondary battery were almost the same as those of Example 1, and good results were obtained.

In the above embodiment, the active material thin film is formed by the sputtering method. However, the present invention is not limited to this, and another thin film forming method such as a CVD method may be used.

[0056]

According to the present invention, an electrode for a lithium secondary battery having a high charge / discharge capacity and excellent charge / discharge cycle characteristics can be stably manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a sputtering apparatus having a rotating holder used in an embodiment according to the present invention.

FIG. 2 is a perspective view showing a lithium secondary battery manufactured in an example according to the present invention.

FIG. 3 is a schematic cross-sectional view showing a lithium secondary battery manufactured in an example according to the present invention.

FIG. 4 is a diagram showing a concentration distribution of a copper element in a depth direction in the electrode of Example 1.

FIG. 5 is a view showing a concentration distribution of a copper element in a depth direction in an electrode of Example 2.

FIG. 6 is a view showing a concentration distribution of a copper element in a depth direction in an electrode of Example 3.

FIG. 7 is a diagram showing a concentration distribution of a copper element in a depth direction in an electrode of Comparative Example 1.

FIG. 8 is a view showing a concentration distribution of a copper element in a depth direction in an electrode of Comparative Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Rotating holder 2 ... Target 3 ... High frequency power supply 4 ... Ar plasma 10 ... Outer body 11 ... Negative electrode collector 12 ... Silicon thin film 13 ... Positive electrode collector 14 ... Positive electrode active material layer 15 ... Separator 16 ... Electrolyte 17 ... Negative electrode tab 18 ... Positive electrode tab

 ──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application 2000-3644 (P2000-3644) (32) Priority date January 12, 2000 (2000.1.12) (33) Priority claim country Japan (JP) (72) Inventor Hiromasa Yagi 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Hisaki Tarui 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Masahisa Fujimoto 2-5-5 Keihanhondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Shin Fujitani 2-5-5, Keihanhondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd. (72) Inventor Masaki Shima 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 5H050 AA07 AA08 BA15 CB11 CB13 DA03 FA19 FA20 GA02 GA24 HA14

Claims (12)

[Claims] An active material thin film made of an active material alloying with lithium is formed on a current collector made of a metal that does not alloy with lithium by using a method of forming a thin film by supplying a raw material from a gas phase. A method for producing an electrode for a lithium secondary battery, wherein the active material is formed at a temperature at which a mixed layer formed by diffusion of the current collector component in the active material thin film near an interface with the current collector is formed. A method for producing an electrode for a lithium secondary battery, comprising forming a thin film. 2. The lithium secondary battery according to claim 1, wherein the formation temperature of the active material thin film is a temperature at which an intermetallic compound of the active material and the current collector component is not formed in the mixed layer. Method for producing electrode for secondary battery. 3. The method for manufacturing an electrode for a lithium secondary battery according to claim 1, wherein the formation temperature of the active material thin film is lower than 300 ° C. 4. The method for manufacturing an electrode for a lithium secondary battery according to claim 1, wherein a heat treatment is performed after forming the active material thin film. 5. The method for manufacturing an electrode for a lithium secondary battery according to claim 4, wherein the temperature of the heat treatment is lower than 650 ° C. 6. The method for manufacturing an electrode for a lithium secondary battery according to claim 1, wherein the active material contains silicon or germanium as a main component. 7. The method of manufacturing an electrode for a lithium secondary battery according to claim 1, wherein the active material thin film is an amorphous silicon thin film or a microcrystalline silicon thin film. 8. The method according to claim 1, wherein the active material thin film is an amorphous germanium thin film, a microcrystalline germanium thin film, an amorphous silicon germanium alloy thin film, or a microcrystalline silicon germanium alloy thin film. A method for producing an electrode for a lithium secondary battery according to any one of the preceding claims. 9. The method for manufacturing an electrode for a lithium secondary battery according to claim 1, wherein at least a surface portion of the current collector contains copper as a main component. 10. The method for producing an electrode for a lithium secondary battery according to claim 1, wherein the method of forming the active material thin film is a sputtering method. 11. The method for producing an electrode for a lithium secondary battery according to claim 1, wherein the formation of the active material thin film on the current collector is performed intermittently. . 12. The current collector is placed on the outer peripheral surface of a drum-shaped holder, and the active material thin film is formed on the current collector while rotating the holder, so that the current collector is intermittently placed on the current collector. The method for manufacturing an electrode for a lithium secondary battery according to claim 11, wherein the active material thin film is formed on the electrode.