Method for manufacturing conductive member, and current collector or separator

Abstract

To provide a conductive member capable of maintaining adhesion between a base material and an active material or a conductive assistant for a long term even without depending on hydrophilicity due to a functional group formed on the surface of the conductive member and having a sheet resistance lower than ever before for a long term.SOLUTION: The method for manufacturing a conductive member comprises: the DLC film deposition step of depositing a DLC film on the surface of a base material by supplying a hydrocarbon based raw material gas to a plasma treatment chamber storing the base material of the conductive member, generating plasma in the plasma treatment chamber and applying a high-voltage pulse to a high-voltage pulse application electrode provided in the base material or the periphery of the base material; and the oxygen treatment step of subjecting the DLC film to oxygen treatment by supplying an oxygen gas to the plasma treatment chamber after the DLC film deposition step, generating plasma in the plasma treatment chamber and applying a high-voltage pulse to the high-voltage pulse application electrode provided in the base material or the periphery of the base material. The surface roughness of the conductive member after the oxygen treatment step is 0.1 μm or more and 0.5 μm or less.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for producing a conductive member that constitutes a current collector or separator used in electrodes of fuel cells, lithium batteries, capacitors, and the like. [Background technology]

[0002] For example, current collectors and separators for fuel cells are made by coating the surface of a metal substrate with a slurry containing an active material and a conductive additive.

[0003] Since the conductive members constituting these current collectors and separators are required to have reduced sheet resistance, it is desirable that the surface properties of the substrate have excellent adhesion to the active material and conductive additive.

[0004] Therefore, in Patent Document 1, in order to improve the adhesive strength between the above-mentioned slurry and the substrate surface, a conductive DLC coating is formed on the surface of the substrate, and a gas containing oxygen and nitrogen is added to the conductive DLC coating to obtain hydrophilic surface properties.Hydrophilicity is obtained 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, which exhibit hydrophilicity.

[0005] However, the hydrophilicity obtained in this manner may result in the functional groups not remaining on the substrate surface for a long period of time because the chemical bonding state may change over time, and 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. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6138007 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the above-mentioned problems all at once, and its main objective is to provide a conductive member with lower sheet resistance than conventional conductive members by making it possible to 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 the substrate surface. [Means for solving the problem]

[0008] That is, the method for producing a conductive member according to the present invention comprises: a DLC film formation step of supplying a hydrocarbon-based source gas into a plasma processing chamber that accommodates a substrate of the conductive member, generating plasma in the plasma processing chamber, and applying a high-voltage pulse to the substrate or an electrode for applying a high-voltage pulse provided around the substrate, thereby forming a DLC coating on the surface of the substrate; and an oxygen treatment step of, after the DLC film formation step, supplying oxygen gas into the plasma processing chamber, generating plasma in the plasma processing chamber, and applying a high-voltage pulse to the substrate or an electrode for applying a high-voltage pulse provided around the substrate, thereby oxygen-treating the DLC coating, wherein the surface roughness of the conductive member after the oxygen treatment step is 0.1 μm or more and 0.5 μm or less.

[0009] 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, which mechanically improves the adhesion between the surface of the conductive member and the active material or conductive additive, and the effect is 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.

[0010] 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=CO bonds to CO 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.

[0011] 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 or conductive additive.

[0012] A more specific embodiment of the oxygen treatment step 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.

[0013] If the oxygen treatment process exceeds 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, so it is preferable that the oxygen treatment process be within 4 minutes.

[0014] In order 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 in the DLC film formation process.

[0015] Specifically, the contact resistance of the DLC coating after the oxygen treatment step is 10 mΩcm. 2 It is preferable that:

[0016] 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 during the DLC film formation process before proceeding to the oxygen treatment process, which activates the oxygen and enhances the effect of the oxygen treatment.

[0017] 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. [Effects of the Invention]

[0018] According to the present invention configured in this manner, it is possible to maintain the adhesion between the substrate and the active material or conductive additive for a long period of time without relying on the hydrophilicity due to the functional groups generated on the surface of the conductive member, and it is possible to provide a conductive member having a lower sheet resistance for a long period of time than conventional conductive members. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic diagram showing the configuration of a plasma processing apparatus according to an embodiment of the present invention; [Figure 2] FIG. 4 is a flowchart showing a method for manufacturing a conductive member according to the embodiment. [Figure 3] 10 is an experimental result showing the correlation between the time of oxygen plasma treatment and the contact resistance value according to the embodiment. [Figure 4] 10 shows the analysis results of chemical bond information on the surface of the conductive member manufactured in this embodiment. [Figure 5] Comparison results of the difference in hydrophilicity between with and without oxygen plasma treatment. [Figure 6] Comparison results of the difference in sheet resistance with and without oxygen plasma treatment. [Figure 7] FIG. 10 is a schematic diagram showing the configuration of a plasma processing apparatus according to another embodiment. [Figure 8]FIG. 10 is a schematic diagram showing the configuration of a plasma processing apparatus according to another embodiment. [Figure 9] FIG. 10 is a schematic diagram showing the configuration of a plasma processing apparatus according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of a method for manufacturing a conductive member according to the present invention will be described below with reference to the drawings.

[0021] The conductive member manufactured by the manufacturing method according to the present invention constitutes a current collector used in, for example, a fuel cell, a lithium battery, a capacitor, etc., and in this embodiment, the manufacture of a conductive member that constitutes a separator for a fuel cell will be described.

[0022] <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 the so-called roll-to-roll type, and as shown in FIG. 1, includes 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.

[0023] The delivery mechanism 10 delivers the substrate Z from a coil material formed by winding the substrate Z, and includes at least a delivery roller 11 on which the coil material is set. The delivery 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 in the plasma treatment described below.

[0024] The plasma processing chamber X is a chamber for performing plasma processing on the substrate Z, and is equipped with a high-frequency antenna 4 to which high-frequency power is applied from a high-frequency power supply 2. The plasma processing chamber X is supplied with plasma raw material gas and maintained at a predetermined pressure.

[0025] In this embodiment, at least two plasma processing chambers X for performing different plasma treatments are provided in series along the transfer 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 treating the front surface of the substrate Z, and the first plasma processing chamber X1 and the second plasma processing chamber X2 for plasma treating the back surface of the substrate Z.

[0026] Specifically, the first plasma treatment chamber X1 is a chamber in which a conductive DLC coating, which is a gas barrier coating having corrosion resistance against 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.

[0027] In this embodiment, the conductive member Z' manufactured by plasma treating the base material Z in this manner is wound up by a winding mechanism 60. The winding mechanism 60 here includes at least a winding roller 61 that winds up the sheet-like conductive member Z' into a coil.

[0028] <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.

[0029] First, the sheet-shaped substrate Z is sent out to the first plasma processing chamber X1 by the sending mechanism 10, and a DLC film 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 supply 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 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.

[0030] 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 overlap 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.

[0031] 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 higher but 10 Pa or lower, preferably 0.5 Pa or higher but 2 Pa or lower. High-frequency power is applied to the high-frequency antenna 4 from the high-frequency power supply 2 via a matching box (not shown), generating a discharge plasma containing oxygen ions near the surface of the substrate Z. A negative pulse voltage of, for example, −2 kV or higher but −500 V or lower, more preferably −1.5 kV or higher but −100 V or lower, is then applied to the substrate Z via the feed roller 11, implanting oxygen ions into the conductive DLC coating, resulting in sputtering. By sputtering with oxygen ions in this manner, the conductive DLC coating, which was 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 four minutes, the surface roughness that had decreased once 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).

[0032] In this embodiment, the above-mentioned DLC film formation process and oxygen treatment process are performed successively while maintaining the vacuum state in 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 successively while maintaining the vacuum state in each of the plasma treatment chambers X1 and X2.

[0033] 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 a component that constitutes a separator, and is the one before the slurry containing the active material and conductive additive is applied.

[0034] <Characteristics of conductive materials> Next, the characteristic configuration of the conductive member manufactured by the above-described manufacturing method will be described.

[0035] 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.

[0036] Furthermore, after the oxygen treatment step, the surface state of this conductive member is such that the ratio of O=CO bonds to CO bonds is 20% or more. Here, the results of analyzing the surface chemical bond information by XPS for samples that were not subjected to the oxygen treatment process (Nos. 1 and 2) and samples that were subjected to the oxygen treatment process (Nos. 3 to 6) are shown in Figure 4. Specifically, this analysis result is the ratio of the peak intensity of the O=CO bond to the peak intensity of the CO bond. As can be seen from the analysis results, the oxygen plasma treatment in the oxygen treatment step improves the ratio of O=CO bonds to CO 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.

[0037] Furthermore, 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, each type of line represents 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 provided 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.

[0038] According to this method for manufacturing a conductive member, the DLC coating is treated with oxygen plasma, and the resulting sputtering effect makes it possible to 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 this 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.

[0039] Furthermore, by performing oxygen plasma treatment, the ratio of O=CO bonds to CO bonds is increased to 20% or more, thereby increasing the ratio of π bonds to σ bonds, thereby enabling a further reduction in sheet resistance.

[0040] Furthermore, oxygen plasma treatment creates functional groups such as hydroxyl groups (-OH groups) and carboxyl groups (-COOH) on the surface of the DLC coating, making it hydrophilic, which improves adhesion between the DLC coating and the slurry used to apply active material and conductive additives. This allows more active material and conductive additives to be applied to the surface of the conductive material, which also contributes to reducing sheet resistance.

[0041] In this way, due to the various effects of the oxygen plasma treatment, the sheet resistance of the conductive member is dramatically reduced compared to conventional methods, and this low sheet resistance can be maintained for a long period of time.

[0042] Here, the sheet resistance was measured for samples (Nos. 4 to 6) that were not subjected to the oxygen treatment process and samples (Nos. 1 to 3, 7) that were subjected to the oxygen treatment process, and the results are shown in Figure 6. The measured value for each sample was measured in a state where no active material was applied. As can be seen from this result, the sheet resistance of the DLC film without oxygen plasma treatment was 10 mΩ cm. 2 On the other hand, the sheet resistance of the DLC film after oxygen plasma treatment was 10 mΩ cm. 2 This shows that oxygen plasma treatment is effective in reducing the sheet resistance.

[0043] The present invention is not limited to the above-described embodiment.

[0044] For example, the plasma processing apparatus 100 is not limited to the configuration described in the above embodiment. It may be configured, as shown in FIG. 7, to include a high-voltage pulse application electrode 7 (mesh electrode) disposed around the substrate Z and 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 in which high-frequency power from a high-frequency power supply and a high-voltage pulse from a high-voltage pulse power supply 3 are simultaneously applied to the mesh electrode. However, as shown in FIG. 8, the plasma processing apparatus may be an inductively coupled plasma (ICP) system in which high-frequency power and a high-voltage pulse are applied 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.

[0045] Furthermore, in the above embodiment, the substrate Z is subjected to plasma treatment while being transported in the vertical direction, but the substrate Z may also be subjected to plasma treatment while being transported, for example, in the horizontal direction.

[0046] 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 film. 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 supply 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 a 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 formation of nuclei may also be achieved by implanting nitrogen ions.

[0047] Additionally, prior to the DLC film formation step, a plasma treatment may be performed to remove the oxide film (Al2O3) from the substrate Z. Specifically, such a plasma treatment may involve argon gas cleaning, in which argon gas is introduced into the plasma treatment chamber X, maintained at 1 Pa, and plasma is generated to remove the oxide film.

[0048] Furthermore, although four plasma processing chambers X are provided in the above embodiment, three plasma processing chambers X may be provided as shown in Fig. 9. Specifically, a first plasma processing chamber X1 for forming a conductive DLC coating on the front surface of the substrate Z, a first plasma processing chamber X1 for forming a conductive DLC coating on the back surface of the substrate Z, and a second plasma processing chamber X2 for performing oxygen plasma treatment on both surfaces of the substrate Z may be provided in this order.

[0049] The substrate Z is not limited to aluminum, and may be made of at least one metal selected from nickel (Ni), iron (Fe), magnesium (Mg), titanium (Ti), and alloys containing these metals.

[0050] Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0051] 100 Plasma treatment device X: Plasma treatment chamber Z...Base material 10. Delivery mechanism 2...High frequency power supply 3. High-voltage pulse power supply 4 Antenna 5. Heater 60 Winding mechanism

Claims

1. 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.

2. 2. The method for producing a conductive member according to claim 1, wherein the surface state 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.

3. 3. The method for manufacturing a conductive member according to claim 1, wherein the pressure of the oxygen gas supplied into the plasma processing chamber in the oxygen treatment step is 0.1 Pa or more and 10 Pa or less.

4. 4. The method for manufacturing a conductive member according to claim 1, wherein the oxygen treatment step is performed for 4 minutes or less.

5. 5. The method for manufacturing a conductive member according to claim 1, wherein the substrate is heated to a temperature of 100 degrees Celsius or higher and 450 degrees Celsius or lower in the DLC film forming step.

6. The contact resistance of the DLC coating after the oxygen treatment step is 10 mΩcm ２ 6. The method for manufacturing a conductive member according to claim 1, wherein the following is true:

7. 7. The method for manufacturing a conductive member according to claim 1, wherein the DLC film forming step and the oxygen treatment step are performed successively while maintaining a vacuum state in the plasma treatment chamber.

8. 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, After the oxygen treatment step, hydrophilic functional groups are formed on the surface of the DLC coating, 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 cm ２ A current collector or separator characterized by:

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