JP6809211B2 - Silicon plating method and manufacturing method of silicon plated metal plate - Google Patents

Description

The present invention relates to a silicon plating method, and more particularly to a silicon plating method by cathode electrolysis using an organic solvent and a method for producing a silicon-plated metal plate.

Lithium-ion secondary batteries are indispensable for portable electronic devices such as mobile phones and notebook computers by taking advantage of their features of being lightweight and having high energy density. Furthermore, as interest in energy issues has increased in recent years, many needs are increasing in various markets such as next-generation vehicles such as electric vehicles and stabilization of power supply systems that utilize natural energy.

As a candidate for a negative electrode active material that enables high energy density, a metal that can occlude lithium such as silicon (hereinafter Si) and tin (hereinafter Sn), or a metal oxide is promising.

For example, Patent Document 1 describes a current collector plate made of a metal foil having discontinuous granular tin plating on at least one side, and the average diameter of the granular tin plating in the direction of the current collector plate surface is 0.5 μm or more and 20 μm. The following is disclosed, and a negative electrode for a lithium ion secondary battery is disclosed in which the lower part of the granular tin plating forms an alloy layer with a metal constituting a current collector plate. The negative electrode for a lithium ion secondary battery disclosed in Patent Document 1 is characterized by having excellent charge / discharge cycle characteristics.

However, while the theoretical capacity of Sn is 994 mAh / g, the theoretical capacity of Si is 4200 mAh / g, and it is more preferable to apply Si as the negative electrode active material from the viewpoint of increasing the energy density.

There is a chemical vapor deposition method as a conventional method for forming a Si film on a current collector of a metal foil, but the problem is that the manufacturing cost is high. Therefore, in Non-Patent Document 1, focusing on the electrolytic precipitation method that can achieve lower cost, 1-Methyl-1-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide having the highest conductivity among TFSI-based ionic liquids. It has been reported that SiCl ₄ is added to the mixture to obtain a Si electrodeposition product with a purity of 97 at.%. However, since the resistivity of the Si electrodeposition is high near room temperature, there is a problem that it is difficult to thicken the electrodeposition and the formation rate is not sufficient.

Therefore, Non-Patent Documents 2 and 3 disclose Si film electrolysis by constant current electrolysis using a molten salt having a temperature higher than that of an ionic liquid. In Non-Patent Document 2, in a system in which K ₂ SiF ₆ is added to 1018 K molten LiF-NaF-KF, Si is electrolyzed by constant current electrolysis by changing the K ₂ SiF ₆ concentration and current density. It has been reported that a film can be formed. Further, in Non-Patent Document 3, in a system in which K ₂ SiF ₆ is added to molten KF-KCl of 923K, the concentration and current density of K ₂ SiF ₆ are changed, and Si electrodeposition is performed by constant current electrolysis. Moreover, it has been reported that a smooth Si film can be formed.

However, in the reported examples of Non-Patent Documents 2 and 3, the plating bath temperature is high, LiF has low solubility in water, and it is difficult to clean after plating. Therefore, the reported examples are applied to industrial mass production. Has many technical issues to be solved.

Patent Document 2 focuses on the fact that silicon has strong hydrophilicity, and focuses on an organic solvent solution of silicon halide or silane halide, an acetic acid solution of ethyl silicate, an organic solvent solution of ammonium silicate, and an organic solvent of potassium silicate. A method of forming an amorphous silicon active layer on a cathode by an electrolytic precipitation method using a solution is disclosed. Further, Patent Document 2 discloses that tetramethylammonium chloride is added as a supporting electrolyte to an electrolytic solution to cause a reduction reaction to precipitate amorphous silicon in order to increase the precipitation rate.

The precipitation method disclosed in Patent Document 2 can form an amorphous silicon layer. However, the amorphous silicon layer is not a dense and smooth silicon layer. As described above, Patent Document 2 does not disclose a method for forming a silicon layer that is denser and smoother than the amorphous silicon layer.

Japanese Unexamined Patent Publication No. 2013-225437 Japanese Unexamined Patent Publication No. 5-55257

Abstracts of the Autumn Meeting of Electrochemistry, vol.2014, p65 (2014) G.M.Rao, D.Elwell, R.S.Feigelson, J.Electrochem.Soc., 127, p1940-1944 (1980) Abstracts of the 46th Molten Salt Chemistry Conference, 39, (2014)

Si cannot be electroplated with an aqueous solution. In consideration of this point, it is an object of the present invention to provide a Si plating method for a metal plate by cathode electrolysis and a method for manufacturing a Si plated metal plate, which can be performed at around room temperature using an organic solvent.

Therefore, the present inventors have diligently studied the effects of organic solvents, silicon sources (hereinafter, also referred to as "Si sources"), conductive agents, plating additives, and energization patterns as follows.

[experimental method]
For the Si electrodeposition experiment, a 3-electrode cell was used, and the following organic electrolyte was used to energize the pulse of N: 0.03A 90ms, OFF: 1000ms 500 times (45 seconds in total), and the copper plate of the cathode. Si electrodeposition was performed on the surface. An electrodeposition experiment was conducted in an Ar atmosphere in order to eliminate the influence of moisture. First, the cathode electrodeposition of Si was performed by cathodic electric field treatment in a system in which dimethyl sulfoxide was used as the organic solvent and tetraethoxysilane was used as the silicon source as the first organic electrolytic solution, and tetramethylammonium chloride was added as the conductive agent. ..

Further, by a cathode electric field treatment in a system in which dimethyl sulfoxide is used as the organic solvent as the second organic electrolytic solution, tetraethoxysilane is used as the silicon source, and ethoxylated α-naphthol sulfonic acid (hereinafter referred to as “ENSA”) is added. , Si was electrodeposited on the cathode.

For comparison, a system using N, N-dimethylformamide as an organic solvent instead of dimethyl sulfoxide of the first organic electrolytic solution (comparative electrolytic solution 1) and a system using acetic anhydride as an organic solvent (comparative electrolytic solution). 2) Cathode electrodeposition of Si was carried out by cathodic electric field treatment in a system using ethylene carbonate as an organic solvent (comparative electrolytic solution 3).

[Experimental result]
The electrodeposition results of the Si foil obtained by the cathode electrolysis treatment using the first organic electrolytic solution are shown in FIGS. 1 (a) and 1 (b). FIG. 1 (a) is an SEM photograph of the Si foil electrodeposited on the copper electrode, and FIG. 1 (b) is an energy dispersive X-ray spectroscopy (Energy dispersive X) of the Si foil electrodeposited on the copper electrode. -ray spectrometry) result. From the semi-quantitative results by SEM / EDX (scanning electron microscope / energy dispersive X-ray spectroscopy), Si and O are almost 1: 1 and O is insufficient for SiO ₂ , so it is metallic Si. The possibility is high.

FIG. 2 shows the electrodeposition results of the Si foil obtained by the cathode electrolysis treatment using the second organic electrolytic solution. As can be seen by comparing FIG. 1A and FIG. 2, the electrodeposited Si formed by using the second organic electrolytic solution is smoother than the electrodeposited Si formed by using the first organic electrolytic solution. is there.

On the other hand, in the comparative electrolytes 1 to 3 used for comparison, no cathode electrodeposition of Si was observed on the copper electrode.

The present invention has been made based on the above findings, and has the following gist of (1) to (9).

(1) Using dimethyl sulfoxide as a solvent, at least one of a silicon compound having an ethoxy group of 75.0 to 280.0 g / L and ammonium silicate 1.0 to 5.0 g / L with respect to the solvent, and the solvent. A plating solution containing 5.0 to 20.0 g / L of a polyoxyethylene compound was prepared, the cathode was immersed in the plating solution, and the cathode was electrolyzed at 15 ° C to 50 ° C. A silicon plating method characterized by forming a silicon layer on the surface of a solvent.
(2) The silicon plating according to (1), wherein the plating solution further contains at least one of tetraalkylammonium chloride and an organic sulfonic acid at 5 to 15 g / L with respect to the solvent. Method.
(3) The silicon plating method according to (1) or (2), wherein tetraethoxysilane is used as the silicon compound having an ethoxy group.
(4) The silicon plating method according to any one of (1) to (3), wherein at least one of ethoxylated α-naphthol sulfonic acid and polyethylene glycol is used as the polyoxyethylene compound.
(5) The silicon plating method according to (2), wherein at least one of tetrabutylammonium chloride, tetrapropylammonium chloride, and tetramethylammonium chloride is used as the tetraalkylammonium chloride.
(6) The silicon plating method according to (2), wherein at least one of methanesulfonic acid, benzenesulfonic acid and phenolsulfonic acid is used as the organic sulfonic acid.
(7) The silicon plating method according to any one of (1) to (6), wherein the temperature of the plating solution is set to 40 ° C. to 50 ° C. and cathode electrolysis is performed.
(8) One of (1) to (7), which comprises using a triode to electrolyze the cathode with the voltage of the cathode set to -0.8 to -2.0 V with respect to the pseudo reference electrode. The silicon plating method described.
(9) Using the cathode, a current with a cathode current density of 0.1 to 5.0 A / dm ² is energized for 0.1 to 4.0 seconds so that the duty ratio becomes 0.1 to 1.0. The silicon plating method according to any one of (1) to (8), wherein a silicon layer is formed on the surface of the cathode by performing constant current pulse electrolysis that repeats the suspension of energization.
(10) A method for producing a silicon-plated metal plate, which comprises forming a silicon layer on the surface of the metal plate using any of the silicon plating methods (1) to (9) using the metal plate as a cathode.

The silicon plating method and the method for producing a silicon-plated metal plate by cathode electrolysis using an organic solvent of the present invention are easy to carry out, and according to the silicon plating method of the present invention, the production cost of silicon plating can be reduced. .. In addition, the production method of the present invention can produce a silicon layer as a light absorption layer of a solar cell at low cost.

(A) is an SEM photograph of a Si foil electrodeposited on a copper electrode using a first organic electrolytic solution, and (b) is an energy dispersive X-ray spectroscopy of the Si foil electrodeposited on a copper electrode. Is the result of. It is an SEM photograph of the Si foil obtained by the cathode electrolysis treatment using the 2nd organic electrolytic solution.

[Si plated metal plate]
The Si-plated metal plate has a structure in which a silicon layer is formed on the surface of the metal plate. The Si-plated metal plate manufactured by the manufacturing method of the present invention will be described in detail below.

The metal plate is not particularly limited, but copper or a copper alloy is preferably used. However, in the case of a steel plate or a stainless alloy plate, since the surface surface thereof has poor adhesion of Si, it is preferable to use one plated with copper, a copper alloy, nickel, silver or the like.

Further, the purity of silicon in the silicon layer is 99% by mass or more. If it is less than 99% by mass, the characteristics as metallic silicon are not satisfied. For example, when the negative electrode active material of a lithium ion battery is used, a high charge / discharge capacity per unit weight of the active material cannot be secured. The amount of silicon adhered is preferably 0.12 mg / cm ² or more and 5 mg / cm ² or less.

[Manufacturing method of Si-plated metal plate]
Next, the method for manufacturing the Si-plated metal plate of the present invention will be described in detail.
First, using dimethyl sulfoxide as a solvent, at least one of a silicon compound having an ethoxy group of 75.0 to 280.0 g / L and ammonium silicate 1.0 to 5.0 g / L with respect to the solvent was added to the solvent. On the other hand, a plating solution containing 5.0 to 20.0 g / L of the polyoxyethylene compound is prepared.

It is preferable to use tetraethoxysilane as the silicon compound having an ethoxy group.

Further, as the polyoxyethylene compound, ethoxylated α-naphthol sulfonic acid and polyethylene glycol are preferable, and one kind or two or more kinds may be used.

Further, the plating solution may contain at least one of tetraalkylammonium chloride and organic sulfonic acid at 5 to 15 g / L with respect to the solvent. As the tetraalkylammonium chloride, tetrabutylammonium chloride, tetrapropylammonium chloride, and tetramethylammonium chloride are preferable, and one kind or two or more kinds may be used. Further, as the tetramethylammonium chloride, tetrabutylammonium chloride, tetrapropylammonium chloride, and tetramethylammonium chloride are preferable, and one kind or two or more kinds may be used. Further, as the organic sulfonic acid, methanesulfonic acid, benzenesulfonic acid and phenolsulfonic acid are preferable, and one kind or two or more kinds may be used.

Cathodic electrolysis of silicon preferably eliminates the influence of moisture as much as possible. Therefore, it is preferable that the plating solution does not contain water. However, since dimethyl sulfoxide has extremely high hygroscopicity, it is desirable to perform cathodic electrolysis treatment in a container filled with an inert gas such as Ar, or to perform cathodic electrolysis treatment in an atmosphere environment of an inert gas such as Ar. .. Further, it is preferable to use a cathode in which the oxide film formed on the metal plate is removed with a weak acid, washed with water and sufficiently dried.

Further, the above-mentioned metal plate is immersed in the plating solution as a cathode, and constant current pulse electrolysis is performed using the metal plate while keeping the plating solution at 15 ° C. to 50 ° C. If the temperature is lower than 15 ° C., the solvent dimethyl sulfoxide solidifies, and plating becomes impossible. On the other hand, even if the temperature exceeds 50 ° C., the amount, shape, and characteristics of the obtained Si plating are not improved, which is a waste of energy cost. The temperature of the plating solution is preferably 40 ° C. to 50 ° C.

In the constant current pulse electrolysis, a constant current having a cathode current density of 0.01 to 3.0 A / dm ² is applied for 0.1 to 3.0 seconds, and then a constant current pulse that suspends the energization is repeatedly applied. Do. If it is less than 0.01 A / dm ² , the electrodeposition of Si is extremely small. On the other hand, when the current density exceeds 3.0 A / dm ² , the deposited Si begins to decrease. If the energization time per pulse is less than 0.1 seconds, Si is hardly electrodeposited. On the other hand, if it exceeds 3.0 seconds, the amount of electrodeposited Si decreases. The ON time with respect to the total of the time for energizing a constant current in one pulse (hereinafter, also referred to as “ON time”) and the time for suspending energization after the ON time (hereinafter, also referred to as “OFF time”). The ratio of time, that is, the duty ratio in one cycle of the constant current pulse is controlled to be 0.5 to 0.94. If it is less than 0.5, the OFF time occupies a long time and the productivity is lowered, but the shape and characteristics of the electrodeposited Si are not improved. On the other hand, if it exceeds 0.94, the deposited Si is elongated and has a shape that easily collapses.

The time for continuously performing the constant current pulse electrolysis depends on the desired film thickness of the silicon layer and the concentration of the Si source, and is not particularly limited. However, from the viewpoint of productivity, it is preferable that the total ON time is 10 to 1800 seconds. By performing constant current pulse electrolysis in the molten salt electrolysis bath under the above conditions, a silicon layer having a film thickness of 1.0 μm to 30.0 μm is adhered at 0.12 mg / cm ² or more and 5 mg / cm ² or less. Can be formed.

The cathode on which the silicon layer is formed by performing constant current pulse electrolysis as described above is then washed with water to remove the molten salt and Si source remaining on the cathode surface, and then sufficiently dried to obtain the Si of the present invention. A plated metal plate is manufactured.

Si plating was performed using a two-electrode electrolytic cell in a closed chamber whose inside was filled with dry Ar gas.

A copper foil having a thickness of 15 μm was used as the plating substrate. As a pre-plating treatment, cathode electrolytic degreasing and washing with water at a current density of 10 A / dm ² in a 10 mass% sodium hydroxide solution at 70 ° C. are followed by immersion pickling in 5 mass% dilute sulfuric acid for 5 seconds, washing with water, and then air blowing. It was dry.

As the plating solution, a silicon compound having an ethoxy group and / or ammonium silicate and a polyoxyethylene compound shown in Table 1 were added to dimethyl sulfoxide as a solvent, and the mixture was stirred and dissolved to form a bath. In some examples, tetraalkylammonium chloride or organic sulfonic acid shown in Table 1 was further added as a supporting electrolyte. The plating solution was dehydrated with a dry molecular sieve (3A 1/16) before being subjected to plating. The plating solution of Example 23 of the present invention was prepared so as to contain tetraethoxysilane and ammonium fluoride at concentrations of 75.0 g / L and 2.5 g / L, respectively.

The plating conditions are as shown in Tables 1-1 to 1-3. Table 2 shows the plating adhesion amount and adhesion of the Si plating obtained in the examples of the present invention and the comparative examples.

To evaluate the smoothness, "Use the electron beam three-dimensional roughness analyzer ERA-3000 manufactured by Elionix Inc. to measure the surface roughness in the range of 30 μm × 30 μm with a magnification of 3000 times and obtain the arithmetic average roughness Sa. , Sa <0.05 μm was ⊚, 0.05 μm ≦ Sa <0.15 μm was ◯, 0.15 μm ≦ Sa <0.50 μm was Δ, and 0.50 μm ≦ Sa was ×.

The amount of Si plating adhered was determined from the fluorescent X-ray intensity using a calibration curve prepared in advance and converted into a thickness. For plating adhesion, use a cutter (NT cutter A-300) to insert 100 grids of 2 mm square that reach the metal plate on the plating surface, and attach cellophane tape (Nichiban cellophane tape (registered trademark) CT-18, width 25 mm). The tape was instantly peeled off perpendicular to the plated surface, and if no Si plating was observed on the tape, it was considered good, and if the peeled Si plating was observed on the tape, it was considered defective.

In each of the examples of the present invention, electrodeposition of Si having a plating thickness of 3.5 μm to 5.0 μm was confirmed. Further, in the example of the present invention, the Si layers formed on the copper foil all had good smoothness and adhesion.

Comparative Example 1 is an example in which sodium fluoride is used as a silicon source. Sodium fluoride was hardly dissolved in the dimethyl sulfoxide solvent, and the plating solution could not be bathed. Comparative Example 2 is an example in which tetraethoxysilane was used as a silicon source at a low concentration. Almost no electrodeposition of Si was observed. Comparative Example 3 is an example in which tetraethoxysilane is used as a silicon source at a high concentration. A part of tetraethoxysilane was not mixed with the dimethyl sulfoxide solvent and separated into two layers. Comparative Example 4 is an example in which methyltrimethoxysilane is used as the silicon source. No electrodeposition of Si was observed. Comparative Example 5 is an example in which ammonium fluoride fluorinated is used as a silicon source at a low concentration. No electrodeposition of Si was observed. Comparative Example 6 is an example in which ammonium fluoride fluorinated is used as a silicon source at a high concentration. Part of ammonium fluoride was not dissolved in the dimethyl sulfoxide solvent. If an insoluble silicon source adheres to the substrate, Si plating does not precipitate on that portion, resulting in poor quality and possible causes of flaws. Therefore, Si plating was stopped.

Comparative Example 7 is an example in which ethoxylated α-naphthol sulfonic acid, which is a polyoxyethylene compound, is used at a low concentration. Almost no electrodeposition of Si was observed. Comparative Example 8 is an example in which the polyoxyethylene compound ethoxylated α-naphthol sulfonic acid was not added. No electrodeposition of Si was observed. Comparative Example 9 is an example in which ethoxylated α-naphthol sulfonic acid, which is a polyoxyethylene compound, is used at a high concentration. The electrodeposition of Si was powdery and the plating adhesion was poor.

Comparative Example 10 is an example in which the bath temperature is low, and solidified in the middle of cooling to a predetermined bath temperature after the construction bath. Comparative Example 11 was an example in which the bath temperature was high, and the adhesion of the obtained Si plating was poor.

The silicon plating method and the method for producing a silicon-plated metal plate by cathode electrolysis using an organic solvent of the present invention are easy to carry out, and according to the silicon plating method of the present invention, the production cost of silicon plating can be reduced. .. In addition, the production method of the present invention can produce a silicon layer as a light absorption layer of a solar cell at low cost.

Claims (9)

Using dimethyl sulfoxide as a solvent, at least one of 75.0 to 280.0 g / L of a silicon compound having an ethoxy group and 1.0 to 5.0 g / L of ammonium silicate with respect to the solvent, and with respect to the solvent. A plating solution containing 5.0 to 20.0 g / L of the polyoxyethylene compound was prepared.
The cathode is immersed in the plating solution and electrolyzed at 15 ° C to 50 ° C.
A silicon plating method characterized by forming a silicon layer on the surface of the cathode. The silicon plating method according to claim 1, wherein the plating solution further contains at least one of tetraalkylammonium chloride and an organic sulfonic acid at 5 to 15 g / L with respect to the solvent. The silicon plating method according to claim 1 or 2, wherein tetraethoxysilane is used as the silicon compound having an ethoxy group. The silicon plating method according to any one of claims 1 to 3, wherein at least one of ethoxylated α-naphthol sulfonic acid and polyethylene glycol is used as the polyoxyethylene compound. The silicon plating method according to claim 2, wherein at least one of tetrabutylammonium chloride, tetrapropylammonium chloride, and tetramethylammonium chloride is used as the tetraalkylammonium chloride. The silicon plating method according to claim 2, wherein at least one of methanesulfonic acid, benzenesulfonic acid and phenolsulfonic acid is used as the organic sulfonic acid. The silicon plating method according to any one of claims 1 to 6, wherein the temperature of the plating solution is set to 40 ° C. to 50 ° C. and cathode electrolysis is performed. Using the cathode, a current with a cathode current density of 0.1 to 5.0 A / dm ² is energized for 0.1 to 4.0 seconds, and the energization is performed so that the duty ratio becomes 0.1 to 1.0. The silicon plating method according to any one of claims 1 to 7 , wherein a silicon layer is formed on the surface of the cathode by performing constant current pulse electrolysis that repeats the pauses. A method for producing a silicon-plated metal plate, which comprises forming a silicon layer on the surface of the metal plate by using the silicon plating method according to any one of claims 1 to 8 using the metal plate as a cathode.