JP7799299B2 - Method for manufacturing conductive member, and current collector or separator - Google Patents

Description

The present invention relates to a method for manufacturing conductive materials that constitute current collectors and separators used in electrodes of fuel cells, lithium batteries, capacitors, etc.

For example, fuel cell current collectors and separators are made by coating the surface of a metal substrate with a slurry containing an active material and a conductive additive.

The conductive materials that make up these current collectors and separators are required to have low sheet resistance, so it is desirable for the surface properties of the substrate to have excellent adhesion to the active material and conductive additive.

In order to improve the adhesive strength between the above-mentioned slurry and the substrate surface, Patent Document 1 describes forming a conductive DLC coating on the surface of the substrate and then adding a gas containing oxygen and nitrogen to the conductive DLC coating to achieve hydrophilic surface properties. Hydrophilicity is achieved in this way because the addition of the above-mentioned gas generates functional groups, such as hydroxyl groups (-OH groups), on the surface of the conductive DLC coating that exhibit hydrophilicity.

However, the hydrophilicity achieved in this way may result in the functional groups not remaining on the substrate surface for a long period of time, as the chemical bonding state may change over time. In such cases, the adhesion between the substrate and the active material or conductive additive may not be maintained for a long period of time.

Patent No. 6138007

The present invention was conceived to solve all of the above problems at once, and its main objective is to provide a conductive member with lower sheet resistance than conventional materials by enabling the adhesion between the substrate and the active material or conductive additive to be maintained over the long term without relying on the hydrophilicity of the substrate surface.

That is, the method for manufacturing a conductive member according to the present invention comprises a DLC film formation process in which a hydrocarbon-based source gas is supplied into a plasma processing chamber that accommodates the substrate of the conductive member, plasma is generated in the plasma processing chamber, and high-voltage pulses are applied to the substrate or to an electrode for applying high-voltage pulses provided around the substrate, thereby forming a DLC coating on the surface of the substrate; and an oxygen treatment process, after the DLC film formation process, in which oxygen gas is supplied into the plasma processing chamber, plasma is generated in the plasma processing chamber, and high-voltage pulses are applied to the substrate or to an electrode for applying high-voltage pulses provided around the substrate, thereby oxygen-treating the DLC coating, wherein the surface roughness of the conductive member after the oxygen treatment process is 0.1 μm or more and 0.5 μm or less.

This method of manufacturing a conductive member generates oxygen plasma and applies a high-voltage pulse, allowing the DLC coating to be sputtered with oxygen ions. As a result, the surface roughness of the conductive member is set to 0.1 μm or more and 0.5 μm or less, thereby mechanically improving the adhesion between the surface of the conductive member and the active material or conductive additive, and the effect is, so to speak, semi-permanent.
This makes it possible to maintain the adhesion between the conductive member and the active material or conductive additive for a long period of time without relying on the hydrophilicity of functional groups, and to provide a conductive member that has a lower sheet resistance than conventional conductive members and that maintains this low sheet resistance for a long period of time.

In order to further reduce the sheet resistance, it is preferable that the surface state of the conductive member after the oxygen treatment step has a ratio of O═C—O bonds to C—O bonds of 20% or more.
With such a configuration, the ratio of π bonds to σ bonds increases, increasing the number of free electrons on the surface of the conductive member, thereby enabling a further reduction in sheet resistance.

The high voltage pulse in the oxygen treatment step is preferably −100 V or more and −2 kV or less.
With this configuration, oxygen ions in the oxygen plasma collide with the DLC coating on the substrate surface with high energy (e.g., 100 eV to 1000 eV), which allows the oxygen treatment to produce a favorable sputtering effect, thereby roughening the surface of the conductive member to an extent that mechanically improves the adhesion between the conductive member and the active material and conductive additive.

A more specific embodiment of the oxygen treatment process is one in which the pressure of the oxygen gas supplied into the plasma treatment chamber is 0.1 Pa or more and 10 Pa or less.

If the oxygen treatment process lasts for more than 4 minutes, the surface roughness that had once decreased tends to increase again, and the surface roughness will not be adequate to ensure adhesion with the active material and conductive additive. Therefore, it is preferable that the oxygen treatment process last for 4 minutes or less.

To prevent hydrogen components, which can reduce the conductivity of the DLC coating, from penetrating into the substrate, it is preferable to heat the substrate to a temperature of 100°C or higher and 450°C or lower during the DLC film formation process.

Specifically, it is preferable that the contact resistance of the DLC coating after the oxygen treatment step is 10 mΩcm ² or less.

It is preferable that the DLC film forming step and the oxygen treatment step are carried out successively while maintaining the vacuum state inside the plasma treatment chamber.
In this case, the temperature can be maintained at an elevated level in the DLC film forming process while proceeding to the oxygen treatment process, so that oxygen can be activated and the effect of the oxygen treatment can be enhanced.

Furthermore, the current collector or separator according to the present invention is a current collector or separator having a substrate and a DLC coating formed on the surface of the substrate, characterized in that the surface roughness of the DLC coating is 0.1 μm or more and 0.5 μm or less.
Even with such a current collector or separator, the adhesion between the substrate and the active material or conductive additive is maintained for a long period of time without relying on the hydrophilicity of the functional group.

The present invention, configured in this way, can maintain the adhesion between the substrate and the active material or conductive additive for a long period of time without relying on the hydrophilicity of functional groups generated on the surface of the conductive member, thereby providing a conductive member with lower sheet resistance over the long term than conventional conductive members.

1 is a schematic diagram showing the configuration of a plasma processing apparatus according to an embodiment of the present invention; FIG. 4 is a flowchart showing a method for manufacturing a conductive member according to the embodiment. 10 is an experimental result showing the correlation between the time of oxygen plasma treatment and the contact resistance value according to the embodiment. 10 shows the analysis results of chemical bond information on the surface of the conductive member manufactured in this embodiment. Comparison results of the difference in hydrophilicity between with and without oxygen plasma treatment. Comparison results of the difference in sheet resistance with and without oxygen plasma treatment. FIG. 10 is a schematic diagram showing the configuration of a plasma processing apparatus according to another embodiment. FIG. 10 is a schematic diagram showing the configuration of a plasma processing apparatus according to another embodiment. FIG. 10 is a schematic diagram showing the configuration of a plasma processing apparatus according to another embodiment.

Below, one embodiment of a method for manufacturing a conductive member according to the present invention will be described with reference to the drawings.

The conductive member manufactured by the manufacturing method of the present invention constitutes a current collector used in, for example, fuel cells, lithium batteries, capacitors, etc., and this embodiment focuses on the manufacture of a conductive member that constitutes a separator for a fuel cell.

<Device configuration>
First, an example of a plasma processing apparatus used in this manufacturing method will be described.
The plasma processing apparatus 100 of this embodiment is of a so-called roll-to-roll type, and as shown in FIG. 1, is equipped with a delivery mechanism 10 that delivers a sheet-like substrate Z made of, for example, aluminum, a plasma processing chamber X that performs plasma processing on the delivered substrate Z, a high-frequency power supply 2 that generates plasma in the plasma processing chamber X, and a high-voltage pulse power supply 3 that applies a high-voltage pulse to the substrate Z, and is configured to transport the substrate Z in the vertical direction.

The feed mechanism 10 feeds the substrate Z from a coil material formed by winding the substrate Z, and includes at least a feed roller 11 on which the coil material is set. This feed roller 11 is electrically connected to the set coil-shaped substrate Z, and a negative high-voltage pulse is applied to it from the high-voltage pulse power supply 3 during the plasma treatment described below.

The plasma processing chamber X is a chamber for plasma processing the substrate Z, and is equipped with a high-frequency antenna 4 to which high-frequency power is applied from a high-frequency power source 2. This plasma processing chamber X is supplied with plasma raw material gas and maintained at a predetermined pressure.

In this embodiment, at least two plasma processing chambers X for performing different plasma treatments are arranged in series along the transport direction of the substrate Z. Hereinafter, the upstream plasma processing chamber X will be referred to as the first plasma processing chamber X1, and the downstream plasma processing chamber X will be referred to as the second plasma processing chamber X2. In this embodiment, as shown in FIG. 1, a total of four plasma processing chambers X are provided: the first plasma processing chamber X1 and the second plasma processing chamber X2 for plasma processing the front surface of the substrate Z, and the first plasma processing chamber X1 and the second plasma processing chamber X2 for plasma processing the back surface of the substrate Z.

Specifically, the first plasma treatment chamber X1 is a chamber in which a conductive DLC coating, which acts as a gas barrier coating that is resistant to corrosion by acids and alkalis, is formed on the substrate Z. The second plasma treatment chamber X2 is a chamber in which the surface of the conductive DLC coating formed in the first plasma treatment chamber X1 is subjected to oxygen plasma treatment.

In this embodiment, the conductive member Z' produced by plasma treating the substrate Z is wound up by a winding mechanism 60. The winding mechanism 60 includes at least a winding roller 61 that winds up the sheet-like conductive member Z' into a coil.

<Manufacturing method>
Next, a method for manufacturing the conductive member Z' using the above-described plasma processing apparatus 100 will be described with reference to the flowchart of FIG.

First, the sheet-shaped substrate Z is sent to the first plasma processing chamber X1 by the sending mechanism 10, and a DLC coating is formed on the substrate Z in the first plasma processing chamber X1 (S2: DLC film forming step).
More specifically, a mixed gas of, for example, methane, acetylene, and nitrogen is supplied as a source gas to the first plasma processing chamber X1, which is maintained at a pressure of 0.1 Pa or more and 1 Pa or less, preferably 0.3 Pa or more and 0.5 Pa or less. High-frequency power is applied to the high-frequency antenna 4 from the high-frequency power source 2 via a matching box (not shown), generating a discharge plasma containing carbon ions near the surface of the substrate Z. To prevent hydrogen components, which could reduce the conductivity of the conductive DLC coating, from penetrating the substrate Z, the heater 5 maintains the substrate Z at a temperature of, for example, 200°C or more and 450°C or less, more preferably 200°C or more and 300°C or less. A negative pulse voltage of, for example, −2 kV or more and −800 V or less, more preferably −2 kV or more and −100 V or less, is applied to the substrate Z via the feed roller 11, thereby forming a conductive DLC coating on the surface of the substrate Z.

Meanwhile, the surface of the substrate Z has irregularities that are repeated at a relatively large period, such as rolling irregularities (for example, about 0.5 μm in height and about 50 μm in width), and finer irregularities that are superimposed on the irregularities (for example, about 0.1 μm in height and about 10 μm in width).
When the above-mentioned conductive DLC coating is formed on the surface of such a substrate Z, the conductive DLC coating is formed along the large-period irregularities, and the fine irregularities on the surface of the substrate Z are buried in the conductive DLC coating, resulting in an increase in the surface roughness value.

After this DLC film formation process, the substrate Z on which the conductive DLC coating has been formed is transported to the second plasma treatment chamber X2, where the conductive DLC coating formed on the surface of the substrate Z is subjected to oxygen plasma treatment (S2: oxygen treatment process).
More specifically, oxygen gas containing oxygen, for example, is supplied as a source gas to the second plasma treatment chamber X2 and maintained at a pressure of 0.1 Pa or more and 10 Pa or less, preferably 0.5 Pa or more and 2 Pa or less. High-frequency power is applied to the high-frequency antenna 4 from the high-frequency power source 2 via a matching box (not shown), generating a discharge plasma containing oxygen ions near the surface of the substrate Z. Then, a negative pulse voltage of, for example, −2 kV or more and −500 V or less, more preferably −1.5 kV or more and −100 V or less, is applied to the substrate Z via the feed roller 11, thereby implanting oxygen ions into the conductive DLC coating and causing sputtering. By sputtering with oxygen ions in this manner, the conductive DLC coating formed along the large-period irregularities gradually becomes flatter, reducing surface roughness. This oxygen treatment process is preferably performed for 4 minutes or less, more preferably 2 minutes or less. If the oxygen treatment process lasts for more than 4 minutes, the surface roughness that had decreased tends to increase again, and the appropriate surface roughness required to ensure adhesion with the active material and conductive additive cannot be obtained, resulting in an increase in contact resistance (see Figure 3).

In this embodiment, the above-mentioned DLC film formation process and oxygen treatment process are performed consecutively while maintaining a vacuum state within the plasma treatment chamber X. Specifically, the plasma treatments in the first plasma treatment chamber X1 and the second plasma treatment chamber X2 are performed consecutively while maintaining a vacuum state within each of the plasma treatment chambers X1 and X2.

Through the DLC film formation process and oxygen treatment process, a conductive member is manufactured that has a substrate Z and a DLC coating formed on the surface of the substrate Z, with the DLC coating having a surface roughness (horizontal arithmetic mean roughness) Ra of 0.1 μm or more and 0.5 μm or less. The conductive member here is the component that makes up the separator, and is the component before the slurry containing the active material and conductive additive is applied.

<Characteristic configuration of conductive member>
Next, the characteristic configuration of the conductive member manufactured by the above-described manufacturing method will be described.

Due to the sputtering effect in the oxygen treatment process described above, the conductive member of this embodiment has a surface roughness Ra of 0.1 μm or more and 0.5 μm or less after the oxygen treatment process, and more preferably a surface roughness of 0.1 μm or more and 0.3 μm or less.

Furthermore, after the oxygen treatment step, the surface condition of this conductive member is such that the ratio of O=C--O bonds to C--O bonds is 20% or more.
Here, the results of analyzing the surface chemical bond information by XPS for samples (Nos. 1 and 2) that were not subjected to the oxygen treatment step and samples (Nos. 3 to 6) that were subjected to the oxygen treatment step are shown in Figure 4. Specifically, this analysis result is the ratio of the peak intensity of the O=C-O bond to the peak intensity of the C-O bond.
As can be seen from these analysis results, the oxygen plasma treatment in the oxygen treatment step improves the ratio of O=C-O bonds to C-O bonds. This ratio is 15% or less for the sample that was not subjected to the oxygen treatment step, but is 20% or more, more specifically, 30% or more for the sample that was subjected to the oxygen treatment step.
This shows that the oxygen plasma treatment improves the ratio of π bonds to σ bonds, thereby reducing the sheet resistance of the conductive member.

Furthermore, the oxygen plasma treatment forms functional groups such as hydroxyl groups (-OH groups) and carboxyl groups (-COOH groups) on the surface of the conductive member, and these functional groups provide hydrophilicity.
To confirm the difference in hydrophilicity due to the presence or absence of an oxygen treatment step (more specifically, the treatment time of the oxygen plasma treatment), the contact angle of a droplet dropped on the surface of a conductive member was measured, and the results are shown in Figure 5. Note that the different types of lines in the graph represent the difference in the elapsed time after the oxygen treatment step, and specifically, the respective types of lines represent the results of measuring the contact angle after 10 days, 11 days, 12 days, 14 days, and 46 days.
As can be seen from these measurement results, the oxygen plasma treatment in the oxygen treatment step significantly reduced the contact angle and achieved hydrophilicity. This hydrophilicity was maintained even when the conductive member was wound around the winding roller 61. Furthermore, even after being unwound from the winding roller 61, the hydrophilicity was maintained for about one month if kept in a dry atmosphere.

According to this method for manufacturing a conductive member, the DLC coating is subjected to oxygen plasma treatment, and the resulting sputtering effect can reduce the surface roughness of the DLC coating to 0.1 μm or more and 0.5 μm or less, thereby mechanically improving the adhesion between the surface of the conductive member and the active material or conductive additive, and the effect is, so to speak, semi-permanent.
This makes it possible to maintain the adhesion between the substrate Z and the active material or conductive additive for a long period of time without relying on the hydrophilicity of functional groups generated on the surface of the conductive member as in the past, and to provide a conductive member with lower sheet resistance for a long period of time than in the past.

In addition, oxygen plasma treatment increases the ratio of O=C-O bonds to C-O bonds to 20% or more, thereby increasing the ratio of π bonds to σ bonds, further reducing sheet resistance.

Furthermore, oxygen plasma treatment forms functional groups such as hydroxyl groups (-OH groups) and carboxyl groups (-COOH) on the surface of the DLC coating, making it hydrophilic. This improves adhesion between the DLC coating and the slurry used to apply the active material and conductive additive. This allows for a larger amount of active material and conductive additive to be applied to the surface of the conductive material, which also contributes to reducing sheet resistance.

In this way, the various effects of oxygen plasma treatment significantly reduce the sheet resistance of the conductive material compared to conventional methods, and this low sheet resistance can be maintained for a long period of time.

The sheet resistance of samples (Nos. 4 to 6) that were not subjected to the oxygen treatment step and samples (Nos. 1 to 3 and 7) that were subjected to the oxygen treatment step are measured and the results are shown in Fig. 6. The measured values for each sample were measured in a state where no active material was applied.
As can be seen from these results, the sheet resistance of the DLC coating without oxygen plasma treatment was ¹⁰ mΩcm2 or more, whereas the sheet resistance of the DLC coating with oxygen plasma treatment was ¹⁰ mΩcm2 or less, indicating that oxygen plasma treatment is effective in reducing sheet resistance.

Note that the present invention is not limited to the above embodiment.

For example, the plasma processing apparatus 100 is not limited to the configuration described in the above embodiment. As shown in FIG. 7, the plasma processing apparatus 100 may include a high-voltage pulse application electrode 7 (mesh electrode) disposed around the substrate Z, and may be configured to apply a high-voltage pulse to the high-voltage pulse application electrode 7. The configuration shown in FIG. 7 is a capacitively coupled plasma (CCP) system configured to simultaneously apply high-frequency power from a high-frequency power supply and a high-voltage pulse from a high-voltage pulse power supply 3 to the mesh electrode. However, as shown in FIG. 8, the plasma processing apparatus 100 may be an inductively coupled plasma (ICP) system configured to apply high-frequency power and a high-voltage pulse independently to the mesh electrode. While the configurations shown in FIGS. 7 and 8 apply a high-voltage pulse to the mesh electrode, the high-voltage pulse may be applied directly to the substrate Z without providing a mesh electrode.

In addition, in the above embodiment, the substrate Z is plasma treated while being transported in the vertical direction, but the substrate Z may also be plasma treated while being transported, for example, horizontally.

Furthermore, prior to the DLC film formation process, nuclei (similar to hair roots) may be formed on the substrate Z to improve the adhesion of the DLC coating. More specifically, a carbon compound gas, such as ammonium cyanide, is supplied as a source gas to the first plasma processing chamber X1 and maintained at 1 Pa. High-frequency power is applied to the high-frequency antenna 4 from the high-frequency power source 2 via a matching box (not shown), generating a discharge plasma containing carbon ions near the surface of the substrate Z. Then, a negative DC voltage or negative pulse voltage is applied to the substrate Z via the aforementioned feed roller 11, implanting carbon ions into the surface of the substrate Z to form nuclei. The nuclei may also be formed by implanting nitrogen ions.

In addition, prior to the DLC film formation step, a plasma treatment may be performed to remove the oxide film (Al ₂ O ₃ ) from the substrate Z. Specifically, such a plasma treatment may be argon gas cleaning, in which argon gas, for example, is introduced into the plasma treatment chamber X and maintained at 1 Pa, and plasma is generated to remove the oxide film.

In addition, while four plasma treatment chambers X were provided in the above embodiment, three plasma treatment chambers X may be provided as shown in FIG. 9. Specifically, a first plasma treatment chamber X1 for forming a conductive DLC coating on the surface of the substrate Z, a first plasma treatment chamber X1 for forming a conductive DLC coating on the back surface of the substrate Z, and a second plasma treatment chamber X2 for performing oxygen plasma treatment on both surfaces of the substrate Z may be provided in this order.

The substrate Z is not limited to aluminum, but may also contain at least one metal selected from the group consisting of nickel (Ni), iron (Fe), magnesium (Mg), titanium (Ti), and alloys containing these metals.

It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the invention.

100: Plasma processing apparatus X: Plasma processing chamber Z: Substrate 10: Delivery mechanism 2: High frequency power source 3: High voltage pulse power source 4: Antenna 5: Heater 60: Winding mechanism

Claims (8)

A method for manufacturing a conductive member, comprising:
a DLC film formation process in which a hydrocarbon-based source gas is supplied into a plasma processing chamber that accommodates a substrate of the conductive member, plasma is generated in the plasma processing chamber, and a high voltage pulse is applied to the substrate or to a high voltage pulse application electrode that is provided around the substrate, thereby forming a DLC film on the surface of the substrate;
an oxygen treatment step, which is performed after the DLC film formation step, by supplying oxygen gas into a plasma treatment chamber, generating plasma in the plasma treatment chamber, and applying a high voltage pulse to a high voltage pulse application electrode provided on the substrate or around the substrate, thereby oxygen-treating the DLC film;
the horizontal arithmetic mean roughness of the conductive member after the oxygen treatment step is 0.1 μm or more and 0.5 μm or less;
The method for producing a conductive member, wherein the high voltage pulse in the oxygen treatment step is −100 V or less and −2 kV or more. The method for manufacturing a conductive member according to claim 1, characterized in that the surface condition of the conductive member after the oxygen treatment step is such that the ratio of O=C-O bonds to C-O bonds is 20% or more. The method for manufacturing a conductive member according to claim 1 or 2, characterized in that the pressure of the oxygen gas supplied into the plasma processing chamber during the oxygen treatment step is 0.1 Pa or more and 10 Pa or less. A method for manufacturing a conductive member according to any one of claims 1 to 3, characterized in that the oxygen treatment process lasts for 4 minutes or less. A method for manufacturing a conductive member according to any one of claims 1 to 4, characterized in that, during the DLC film formation process, the substrate is heated to a temperature of 100°C or higher and 450°C or lower. 6. The method for manufacturing a conductive member according to claim 1, wherein the contact resistance of the DLC coating after the oxygen treatment step is 10 mΩcm ^<2 > or less. A method for manufacturing a conductive member according to any one of claims 1 to 6, characterized in that the DLC film formation process and the oxygen treatment process are performed consecutively while maintaining a vacuum state in the plasma treatment chamber. a current collector or separator manufactured through a DLC film formation process in which a hydrocarbon-based source gas is supplied into a plasma treatment chamber accommodating a substrate of a conductive member, plasma is generated in the plasma treatment chamber, and a negative high voltage pulse of −2 kV or more and −100 V or less is applied to the substrate or an electrode for applying a high voltage pulse provided around the substrate, thereby forming a DLC film on a surface of the substrate; and an oxygen treatment process in which, after the DLC film formation process, oxygen gas is supplied into the plasma treatment chamber, plasma is generated in the plasma treatment chamber, and a high voltage pulse is applied to the substrate or an electrode for applying a high voltage pulse provided around the substrate, thereby injecting oxygen ions into the DLC film and sputtering the DLC film,
the current collector or separator has a substrate and a DLC coating formed on the surface of the substrate,
a current collector or separator characterized in that hydrophilic functional groups are formed on the surface of the DLC coating after the oxygen treatment step, the horizontal arithmetic mean roughness of the surface of the DLC coating is 0.1 μm or more and 0.5 μm or less, and the contact resistance of the DLC coating is 10 mΩ· ^cm2 or less.