High-specific-volume tantalum foil material, preparation method and application thereof, and tantalum electrolytic capacitor

Abstract

The invention discloses a high-specific-volume tantalum foil material, a preparation method and application thereof and a tantalum electrolytic capacitor, and relates to the technical field of electrode materials, and the preparation method of the high-specific-volume tantalum foil material comprises the following steps: (1) preparing tantalum powder into a thin film through a solution film forming method; and (2) wrapping the film with a tantalum foil, and sequentially carrying out flash evaporation cladding, electrochemical etching and anodic oxidation to obtain the tantalum foil material with high specific volume. According to the method, the tantalum powder is successfully cladded on the tantalum foil by adopting a method of combining a flash cladding technology and electrochemical etching, so that the specific capacity of the tantalum foil is greatly improved, and compared with untreated commercial tantalum foil, the specific capacity is improved by more than 10 times, a new thought and a new direction are provided for the development of anode materials of tantalum electrolytic capacitors, and the method is suitable for industrial production. Wide application prospects are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a high-specific-capacitance tantalum foil material, a preparation method and application thereof, and a tantalum electrolytic capacitor. Background Art

[0002] With the miniaturization and advancement of high-performance electronic products, tantalum capacitors, with their excellent electrical properties and ultra-high reliability, have attracted significant attention among electronic components. They play key roles in filtering, DC isolation, and instantaneous high-power supply, and are widely used in military and civilian applications such as radar, aerospace, communications, and automotive electronics. Tantalum electrolytic capacitors, studied for their high capacitance and stability, have been marketed for over half a century and have a wide range of applications. However, precisely because of tantalum's extremely high physical and chemical stability, increasing the specific capacitance of tantalum electrolytic capacitor anode materials has been a significant challenge.

[0003] Currently, methods for preparing tantalum electrolytic capacitor anode materials include traditional sintering, screen printing, and electrochemical etching. Compared to traditional tantalum powder sintering, electrochemical etching offers lower costs and a simpler manufacturing process. The electrochemical etching of tantalum foil to produce high-capacity thin-film tantalum electrolytic capacitors holds great promise for the flexibility and miniaturization of electronic devices. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a high specific capacitance tantalum foil material and a preparation method thereof, and to successfully prepare a high specific capacitance tantalum foil material by combining flash cladding technology and electrochemical etching, and to realize the application of the high specific capacitance tantalum foil material as an anode material for tantalum electrolytic capacitors.

[0005] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0006] A first object of the present invention is to provide a method for preparing a high specific capacitance tantalum foil material, comprising the following steps:

[0007] (1) forming a continuous coating of tantalum powder on tantalum foil;

[0008] (2) Wrapping the tantalum foil with tantalum powder coating prepared in step (1) with tantalum foil and then sequentially performing cladding, electrochemical etching and anodizing to obtain a high specific capacity tantalum foil material.

[0009] In step (1), the tantalum foil is pretreated with a first solvent and a base before use; the first solvent includes, but is not limited to, at least one of organic solvents with good oil dissolving ability, such as acetone, benzene, toluene, gasoline, and kerosene; and the base includes, but is not limited to, at least one of strong bases, such as potassium hydroxide and sodium hydroxide. The purpose of the pretreatment is to remove oil and tantalum pentoxide from the surface of the tantalum foil. The pretreatment can be performed with the assistance of ultrasound to improve the pretreatment efficiency.

[0010] In step (1), the coating can be formed by a solution film forming method, wherein the preparation method comprises: dispersing tantalum powder in a second solvent to form a tantalum powder solution, then uniformly coating the tantalum powder solution on the tantalum foil, and drying to form a coating. During the preparation of the tantalum powder solution, the tantalum powder can be rapidly dissolved or uniformly dispersed in the solvent by stirring, shaking, ultrasound, or the like.

[0011] Furthermore, the second solvent includes but is not limited to at least one of volatile solvents such as isopropanol, methanol, and ethanol.

[0012] Furthermore, the concentration of the tantalum powder solution is 2.5-22.5 wt%.

[0013] Furthermore, the coating method of the tantalum powder solution includes but is not limited to at least one of spraying, dipping, brushing, roller coating, and scraping.

[0014] In step (2), the cladding utilizes flash Joule heating technology, and the coated tantalum foil is wrapped with tantalum foil and then sandwiched between graphite paper. The graphite paper is then placed at both ends of the flash electrode and clamped, and tantalum powder cladding is performed after vacuuming.

[0015] Furthermore, the flash cladding voltage is 15-20V, the flash current is 380-400A, and the flash time is 6-8s. Cladding utilizes the instantaneous high temperature generated by flash Joule heating technology to cause the tantalum powder on the tantalum foil to melt with low deformation, forming a dense porous structure.

[0016] In step (2), the electrochemical etching uses a pulsed direct current with a frequency of 30 to 60 Hz, an etching voltage of 3 to 7 V, an etching time of 15 to 35 minutes, a duty cycle of 20 to 50%, an etchant of a lithium chloride-methanol solution with a concentration of 1 to 5 wt%, and a counter electrode of a graphite electrode. The tantalum foil coated with tantalum powder is electrochemically etched using a pulsed direct current power supply to further expand the pores on the surface of the tantalum foil and to effectively etch the pores blocked during melting, thereby forming a larger specific surface area.

[0017] In step (2), the anodic oxidation is performed using a phosphoric acid solution having a concentration of 0.1 to 0.3 wt%, a voltage of 80 to 100 V, and a duration of 10 to 20 minutes. The counter electrode is a platinum sheet electrode. The purpose of the anodic oxidation is to in-situ grow a layer of tantalum pentoxide on the surface of the tantalum foil, thereby obtaining a high-specific capacitance tantalum foil material.

[0018] The second object of the present invention is to provide a high specific capacitance tantalum foil material prepared by the aforementioned preparation method.

[0019] A third object of the present invention is to provide application of the aforementioned high specific capacitance tantalum foil material in tantalum electrolytic capacitors.

[0020] A fourth object of the present invention is to provide a tantalum electrolytic capacitor using the aforementioned high specific capacitance tantalum foil material as the positive electrode material.

[0021] The beneficial effects of the present invention are:

[0022] (1) This invention successfully clads tantalum powder onto tantalum foil using a combination of flash cladding technology and electrochemical etching, significantly increasing the specific capacitance of the tantalum foil. Compared to untreated tantalum foil, the specific capacitance of the tantalum foil is increased by more than 10 times, providing new ideas and directions for the development of anode materials for tantalum electrolytic capacitors and promising broad application prospects.

[0023] (2) The preparation method of the high specific capacitance tantalum foil material provided by the present invention has the advantages of adjustable parameters, simple process, good effect, etc., and is suitable for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM image of the tantalum foil after flash cladding of tantalum powder in Comparative Example 1;

[0025] Figure 2 This is the XPS graph of the commercial tantalum foil in Comparative Example 1;

[0026] Figure 3 This is the XPS graph of the tantalum foil after flash cladding of tantalum powder in Comparative Example 1;

[0027] Figure 4 The XRD patterns of the commercial tantalum foil and the tantalum foil after flash cladding of tantalum powder in Comparative Example 1 are shown below:

[0028] Figure 5 This is the SEM image of the tantalum foil after flash cladding of tantalum powder in Comparative Example 1;

[0029] Figure 6 The Tafel diagram of tantalum foil after flash cladding of tantalum powder solutions with different concentrations;

[0030] Figure 7 The EIS graph of tantalum foil after flash cladding of tantalum powder solutions with different concentrations;

[0031] Figure 8 The specific capacity diagram of tantalum foil after flash evaporation and cladding of tantalum powder and etching for 20 minutes at different etching voltages;

[0032] Figure 9 The specific capacity diagram of tantalum foil after flash evaporation and cladding of tantalum powder at different etching times at an etching voltage of 5V;

[0033] Figure 10 This is an SEM image of the tantalum foil after etching for 30 minutes at an etching voltage of 5 V in Example 8. DETAILED DESCRIPTION

[0034] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to specific embodiments and illustrations.

[0035] Comparative Example 1

[0036] (1) A commercial tantalum foil (2 cm × 2 cm) was ultrasonically treated in acetone for 15 min to remove oil stains on the surface of the tantalum foil. The tantalum foil was then cleaned with ethanol and dried in an oven at 60°C. The tantalum foil was then immersed in a 10 wt% potassium hydroxide solution (95°C) for 1 min to remove tantalum pentoxide from the surface of the tantalum foil. The foil was then rinsed with deionized water and dried in an oven at 60°C to complete the pretreatment of the tantalum foil.

[0037] (2) Tantalum powder (particle size 50 nm) is prepared into a tantalum powder solution with a concentration of 20 wt% using isopropyl alcohol. The solution is ultrasonically treated for 30 min to uniformly disperse the tantalum powder particles in the isopropyl alcohol. The tantalum powder solution is then sprayed onto the tantalum foil pretreated in step (1). After the isopropyl alcohol evaporates, a coating layer covered with tantalum powder particles is formed on the surface of the tantalum foil.

[0038] (3) Wrap the tantalum foil with tantalum powder coating prepared in step (2) with two pieces of tantalum foil and clamp them with pliers to completely seal them on all sides. Then, clamp them between two pieces of graphite paper with a size of 92 mm × 35 mm × 0.7 mm. Place the graphite paper at both ends of the flash electrode and clamp them. After vacuuming, use a flash evaporation device to induce tantalum powder cladding. The flash evaporation voltage is 15 V, the flash evaporation current is 390 A, and the flash evaporation time is 6 s.

[0039] (4) In a two-electrode system, a tantalum foil (2 cm × 2 cm) prepared by flash evaporation and coating tantalum powder in step (3) was used as a working electrode, a graphite sheet (2 cm × 2 cm) was used as a counter electrode, and a 0.1 wt% phosphoric acid solution was used as an electrolyte solution. The system was operated at a constant voltage of 100 V for 10 min to in situ grow a layer of tantalum pentoxide on the surface of the tantalum foil, thereby obtaining a high specific capacity tantalum foil material.

[0040] In order to test the electrochemical performance of tantalum foil, the tantalum foil was pre-immersed in H2SO4 electrolyte (concentration of 1M) for 60 minutes to allow the reaction sites on its surface to fully contact the electrolyte. Then, a double electrode capacitance test was performed, and a Pt sheet (2cm×2cm) was selected as the counter electrode. S -D module and directly record the instrument readings and calculate the area specific capacity. The calculation formula is shown below.

[0041] Cs=C / S

[0042] Where C is directly read by the digital bridge (nF), S is the actual area of tantalum foil in the electrolyte (mm 2 ), C S is the area specific capacity (nF / mm 2 ).

[0043] After testing, the specific capacity of commercial tantalum foil after pretreatment in step (1) is 21.3nF / mm 2 .

[0044] Figure 1 This is the SEM image of the tantalum foil after flash cladding of tantalum powder in Comparative Example 1. Figure 1 It can be seen that the tantalum powder particles are evenly covered on the tantalum foil, and the tantalum powder particles clad on the tantalum foil form a stable and complete structure.

[0045] Figure 2 This is the XPS graph of the commercial tantalum foil in Comparative Example 1. Figure 3 This is the XPS graph of the tantalum foil after flash evaporation and cladding of tantalum powder in Comparative Example 1. Figure 2 and Figure 3 It can be seen that the Ta atomic content of the tantalum foil after flash cladding of tantalum powder is slightly reduced, and the Ta2O5 content is slightly increased.

[0046] Figure 4 The XRD patterns of commercial tantalum foil and tantalum foil after flash evaporation cladding of tantalum powder in comparative example 1 are shown in Figure 1. Figure 4 It can be seen that the Ta2O5 content of the tantalum foil after flash cladding of tantalum powder is slightly increased, and the Ta metal peak is slightly reduced.

[0047] Figure 5 This is the SEM image of the tantalum foil after flash cladding of tantalum powder in Comparative Example 1. Figure 5 It can be seen that after tantalum powder cladding, a smoother and more uniform porous structure is formed on the surface of the tantalum foil, and its surface pores are smaller.

[0048] Comparative Examples 2 to 6

[0049] The method of Comparative Example 1 was followed, except that the concentration of the tantalum powder solution in step (2) was changed, as shown in Table 1.

[0050] Table 1

[0051] Tantalum powder solution concentration (wt%) <![CDATA[Specific capacitance (nF / mm 2 ) <!-- 3 -->]]> Comparative Example 1 20 173.5 Comparative Example 2 2.5 143.3 Comparative Example 3 7.5 157.8 Comparative Example 4 12.5 169.2 Comparative Example 5 17.5 186.4 Comparative Example 6 22.5 159.7

[0052] As can be seen from Table 1, as the concentration of the tantalum powder solution increases, the specific capacity shows a trend of first increasing and then decreasing. This is because when the concentration of the tantalum powder solution is low, some areas on the surface of the tantalum foil are not covered by the tantalum powder, and the specific surface area of the tantalum foil cannot be effectively increased; when the concentration of the tantalum powder solution is high, the tantalum powder on the surface of the tantalum foil will agglomerate, resulting in a decrease in the specific surface area of the tantalum foil. Among them, when the concentration of the tantalum powder solution gradually increases from 2.5wt% to 17.5wt%, the specific capacity of the tantalum foil gradually increases; when the concentration of the tantalum powder is greater than 17.5wt%, the specific capacity of the tantalum foil gradually decreases; when the concentration of the tantalum powder solution is 17.5wt%, the specific capacity reaches a maximum value of 186.4nF / mm 2 In addition, compared with commercial tantalum foil without tantalum powder coating (specific capacitance of 21.3nF / mm 2 ), the specific capacity of tantalum foil can be significantly improved by tantalum powder cladding.

[0053] Figure 6 The Tafel diagram of tantalum foil after flash cladding of tantalum powder solutions with different concentrations. Figure 6 It can be seen that with the increase of tantalum powder concentration, the Tafel curve gradually shifts to the right, and the etching voltage of tantalum foil gradually increases, indicating that the increase of tantalum powder concentration makes the etching difficulty of tantalum foil more difficult.

[0054] Figure 7 The EIS graphs of tantalum foil after flash cladding of tantalum powder solutions with different concentrations are shown in Figure 2. Figure 7 It can be seen that as the concentration of tantalum powder increases, the ability of tantalum foil to block electrons increases, indicating that the difficulty of etching tantalum foil increases.

[0055] Examples 1 to 5

[0056] The method of Comparative Example 1 was followed, except that the concentration of the tantalum powder solution in step (2) was adjusted to 17.5 wt %, and the tantalum foil after flash evaporation and cladding of tantalum powder in step (3) was subjected to electrochemical etching. A pulsed DC power supply was used with a frequency of 50 Hz and a duty cycle of 30%. The etchant was a lithium chloride-methanol solution with a concentration of 3 wt %. The counter electrode was a graphite electrode. The etching time was 20 min. The etching voltage was changed, as shown in Table 2.

[0057] Table 2

[0058] Etching voltage (V) <![CDATA[Specific capacitance (nF / mm 2 )]]> Example 1 5 223.7 Example 2 3 194.7 Example 3 4 205.5 Example 4 6 216.9 Example 5 7 207.2

[0059] Figure 8 This is the specific capacity diagram of tantalum foil after flash evaporation and cladding of tantalum powder and etching for 20 minutes at different etching voltages. Figure 8As shown in Table 2, with the increase of etching voltage, the specific capacity of tantalum foil first increases and then decreases, and the specific capacity of tantalum foil reaches the highest when the etching voltage is 5V.

[0060] Examples 6 to 9

[0061] The method of Example 1 was followed, except that the etching time was changed, as shown in Table 3.

[0062] Table 3

[0063]

[0064]

[0065] Figure 9 This is a graph showing the specific capacity of tantalum foil after flash evaporation and cladding of tantalum powder and etching at different times at an etching voltage of 5V. Figure 9 As shown in Table 3, with the increase of etching time, the specific capacity of tantalum foil first increases and then decreases, and the specific capacity of tantalum foil reaches the highest when the etching time is 30 minutes.

[0066] Figure 10 is a SEM image of the tantalum foil after electrochemical etching in Example 8. Figure 10 It can be seen that after etching at 5V for 30min, the pores on the surface of the tantalum foil are larger and significantly rougher, thus providing a larger specific surface area.

[0067] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high specific capacitance tantalum foil material, characterized in that: The following steps are involved: (1) forming a continuous coating of tantalum powder on tantalum foil; (2) Wrapping the tantalum foil with tantalum powder coating prepared in step (1) with tantalum foil and then sequentially performing cladding, electrochemical etching and anodizing to obtain a high specific capacity tantalum foil material.

2. The preparation method according to claim 1, wherein: In step (1), the tantalum foil is pretreated with a first solvent and a base before use; Preferably, the first solvent is at least one of acetone, benzene, toluene, gasoline, and kerosene; Preferably, the base is at least one of potassium hydroxide and sodium hydroxide.

3. The preparation method according to claim 1, wherein: In step (1), the coating is prepared by a solution film forming method, wherein tantalum powder is dispersed in a second solvent to form a tantalum powder solution, and then the tantalum powder solution is uniformly coated on the tantalum foil, and dried to form a coating; Preferably, the second solvent is at least one of isopropanol, methanol, and ethanol; Preferably, the concentration of the tantalum powder solution is 2.5 to 22.5 wt %; Preferably, the tantalum powder solution is coated by at least one of spraying, dipping, brushing, roller coating, and scraping.

4. The preparation method according to claim 1, wherein: In step (2), the cladding utilizes flash Joule heating technology, and the coated tantalum foil is wrapped with tantalum foil and then sandwiched between graphite paper. The graphite paper is then placed at both ends of the flash electrode and clamped, and tantalum powder cladding is performed after vacuuming.

5. The preparation method according to claim 4, characterized in that: The flash evaporation voltage of the cladding is 15-20V, the flash evaporation current is 380-400A, and the flash evaporation time is 6-8s.

6. The preparation method according to claim 1, wherein: In step (2), the electrochemical etching adopts pulsed direct current with a frequency of 30 to 60 Hz, an etching voltage of 3 to 7 V, an etching time of 15 to 35 min, a duty cycle of 20 to 50%, an etchant of a lithium chloride-methanol solution with a concentration of 1 to 5 wt%, and a counter electrode of a graphite electrode.

7. The preparation method according to claim 1, wherein: In step (2), the anodic oxidation adopts a phosphoric acid solution with a concentration of 0.1 to 0.3 wt%, a voltage of 80 to 100 V, a running time of 10 to 20 minutes, and a platinum sheet electrode as the counter electrode.

8. A high specific capacitance tantalum foil material prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the high specific capacitance tantalum foil material according to claim 8 in tantalum electrolytic capacitors.

10. A tantalum electrolytic capacitor using the high specific capacitance tantalum foil material according to claim 8 as a positive electrode material.

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