A method for preparing a niobium-tantalum composite capacitor anode

Abstract

The application relates to a preparation method of a niobium-tantalum composite capacitor anode, which comprises the following steps: (S1) ball milling niobium powder with D50 being 25-35 mu m and a span being less than or equal to 0.8, tantalum powder with D50 being 4-7 mu m and a span being less than or equal to 0.8, and a binder to obtain niobium-tantalum mixed powder, wherein the binder is a compound of polyvinyl alcohol and polyethylene glycol; (S2) pressing the niobium-tantalum mixed powder into a blank block with a tantalum wire lead-out line, vacuum sintering to obtain a sintered block; (S3) energizing the sintered block in an acid-containing electrolyte to obtain a niobium-tantalum composite capacitor anode. Through the tantalum powder and the niobium powder with different particle sizes, the specific ball milling process and the specific binder, after being pressed into a shape, the composite material obtained after vacuum sintering and energizing processes is used as the anode of the capacitor, and excellent comprehensive performance is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of capacitors, in particular to a preparation method of a niobium-tantalum composite capacitor anode. BACKGROUND

[0002] Niobium (Nb) and tantalum (Ta) belong to valve metals, and are widely used in the manufacture of electrolytic capacitors due to their excellent dielectric properties and chemical stability. Tantalum capacitors use solid electrolytes, providing higher stability and longer service life. They are known for miniaturization, high capacitance, low ESR, high voltage resistance, and good temperature characteristics, maintaining stable performance in a wide temperature range of -50℃ to 100℃, providing large capacitance in a small volume, suitable for circuit design with limited space. In addition, tantalum capacitors maintain good filtering and bypass performance in high-frequency applications. However, tantalum is expensive. The global proven tantalum reserves are only about 308,000 tons, while the reserves of niobium, also a valve metal, are as high as 48,810,000 tons; the price of tantalum is more than 20 times that of niobium. Due to the cost of tantalum, tantalum-based capacitors have been used in high-end markets such as military and aerospace for a long time. If part of the tantalum can be replaced by niobium to reduce the manufacturing cost of the capacitor, it is a problem that needs to be solved.

[0003] There are reports on niobium-tantalum composite capacitors in the prior art. For example, CN106409510A discloses a niobium-tantalum composite capacitor, which is prepared by mixing niobium powder and tantalum powder, then segmentally energizing, and combining graphene oxide-multi-walled carbon nanotube-ruthenium trichloride composite material to prepare a niobium-tantalum composite capacitor with large capacitance and good stability. However, the preparation process of this patent is complex, and multiple steps are required to prepare graphene oxide-highly hydrophilic multi-walled carbon nanotube-ruthenium trichloride composite material as a cathode material, which is not only complicated, but also uses expensive graphene, carbon nanotubes, and noble metal ruthenium, and is not suitable for industrial production.

[0004] CN101859649A discloses a preparation method of a solid electrolyte niobium-tantalum composite capacitor, which is prepared by mixing niobium and tantalum. First, tantalum powder and niobium powder or tantalum powder and pure niobium monoxide are mixed uniformly in a certain proportion, wherein the tantalum content is 5% to 95%, and the remaining content is niobium; then it is pressed into shape to obtain a composite metal anode block, and then vacuum sintering is performed to obtain the anode of the composite capacitor. After electrochemical oxidation, a composite tantalum oxide and niobium oxide dielectric film is formed, becoming the anode of the niobium-tantalum composite capacitor, and the cathode uses solid manganese dioxide. The product is similar in shape to a sheet-type solid electrolyte niobium-tantalum composite capacitor. The preparation method includes the mixing of tantalum powder and niobium powder or niobium monoxide, shaping, sintering, energizing, and coating processes.

[0005] But the above-mentioned patents are physically mixed with tantalum and niobium, which is easy to produce segregation in the pressing process, so that the proportion of niobium and tantalum in the obtained composite capacitor is different, causing heterogeneous interface. It can be considered that in the conventional composite process, due to the problem of dielectric performance and interface compatibility, niobium and tantalum are easy to cause poor stability of the composite material.

[0006] CN104379792A discloses a kind of capacitor grade tantalum niobium alloy wire material and its preparation method, which is to divide niobium powder into two parts, all tantalum powder and first part niobium powder are mixed by gradually increasing the speed, then the second part niobium powder is added, the speed is increased, and the powder material for capacitor grade tantalum niobium alloy is obtained. The patent process avoids the uneven phenomenon caused by excessive addition of niobium powder at one time. However, the inventors found that the reason for poor dispersion of niobium and tantalum in niobium-carbon composite capacitor is not only the unevenness in powder mixing, but also the difference in shrinkage behavior during sintering of the two; and in the subsequent energizing process, due to the difference in oxidation potential, the oxidation degree may be different in different regions of the composite material, causing oxygen vacancy defects, and it is difficult to form a uniform and complete dielectric film on the surface of the niobium-tantalum composite anode. It leads to the defects of large leakage current, high loss and poor high temperature stability. SUMMARY

[0007] To solve the problem of poor dispersion of niobium and tantalum in niobium-tantalum composite capacitor in the prior art, which makes it difficult for the obtained composite capacitor to play the advantages of the two materials, resulting in poor performance, especially large leakage current. The present application provides a niobium-tantalum composite capacitor and its preparation method. By using tantalum powder and niobium powder with different particle sizes, specific ball milling process and specific adhesive, the obtained composite material after vacuum sintering and energizing process is used as the anode of the capacitor, and excellent comprehensive performance is achieved. Specifically, the present application provides the following technical solutions to solve the above technical problems:

[0008] A preparation method of a niobium-tantalum composite capacitor anode, comprising the following steps:

[0009] (S1) D50 is 25-35 μm, and the span of the niobium powder is ≤0.8, D50 is 4-7 μm, and the span of the tantalum powder is ≤0.8, and the adhesive is a mixture of polyvinyl alcohol and polyethylene glycol;

[0010] (S2) The niobium-tantalum mixed powder is pressed into a blank with a tantalum wire lead-out line, vacuum sintered, and a sintered block is obtained;

[0011] (S3) The sintered block is energized in an acid-containing electrolyte to obtain a niobium-tantalum composite capacitor anode.

[0012] Further, in step (S1), the definition of span is Span=(D90-D10) / D50, the smaller the span, the more concentrated the particle size distribution. The number average molecular weight of polyvinyl alcohol is 20-30 million, and the number average molecular weight of polyethylene glycol is 1600-3000. The use of two adhesives with different molecular weights can better improve the performance of the product capacitor, especially to reduce the low leakage current and dielectric loss. It shows that the two adhesives may have some synergistic effect. The high molecular weight polyvinyl alcohol can form a coating film on the surface of the particles, reducing the unevenness caused by transition cold welding. The low molecular weight polyethylene glycol has lubricating and dispersing functions. Polyvinyl alcohol needs a higher molecular weight, not only as an adhesive, but also through the space steric effect of the high molecular chain, to inhibit the gravity stratification caused by the different densities of niobium and tantalum. However, the molecular weight of polyvinyl alcohol should not be too high, otherwise there will be residues in the vacuum sintering stage, affecting the performance of the capacitor. The low molecular weight polyethylene glycol can play a role similar to a "lubricant" during the ball milling stage, inserting between the long chain of polyvinyl alcohol and the metal powder, i.e. preventing excessive cold welding and improving the flowability of ball milling.

[0013] Further, in step (S1), the mass ratio of niobium powder, tantalum powder and adhesive is 70-80:10-15:3.2-4.7, more preferably, the mass ratio of niobium powder to tantalum powder is less than 6:1; the adhesive is a compound of polyvinyl alcohol and polyethylene glycol with a mass ratio of 5-7:1. The ratio of niobium and tantalum should be appropriate to exert the respective advantages of the two materials as capacitor raw materials. The amount of adhesive should not be too high, otherwise too many pores will be caused during subsequent sintering to remove the adhesive, which is not conducive to the performance of the capacitor. After ball milling, the initial particle size of niobium powder is larger, and the ductility of niobium is better, so it mainly breaks under the impact of ball milling energy; tantalum powder is hard and has a small initial particle size, so it is more prone to cold welding and agglomeration during ball milling. After final ball milling, the particle sizes of the two materials are close and uniformly mixed.

[0014] Further, in step (S1), the ball-to-material ratio of ball milling is 5-8:1, the rotation speed is 150-400 rpm, the ball milling time is 3-4 h, the ball medium is zirconia, and the diameter is 4-6 mm.

[0015] Further, in step (S1), the ball milling is segmented ball milling, first adding the niobium powder and polyvinyl alcohol for high-speed ball milling at a speed of 300-400 rpm for 1-2 h, then adding the tantalum powder and polyethylene glycol, reducing the speed to 150-200 rpm, and continuing the ball milling for 2-3 h. The inventors unexpectedly found that the segmented ball milling, combined with the addition of different binders in different stages, can realize the performance improvement of the super-conventional mixed ball milling by precisely controlling the ball milling conditions of different powders and the addition sequence of the binders. The possible reason is that the large-particle-size niobium powder is broken under the high-speed ball milling condition, coated with PVA, and then the small-particle-size tantalum powder and low-molecular-weight polyethylene glycol are added, which can significantly improve the dispersity of niobium and tantalum in the obtained mixed powder.

[0016] Further, in step (S2), the density of the compact is controlled to be 6.8-7.5 g / cm 3 ; the vacuum sintering is pre-sintering at 1300-1500℃ for 0.5-1 h under a vacuum condition of 1×10 -3 to 1×10 -2 Pa, then sintering at 1800-2000℃ for 1-2 h, then cooling to room temperature and returning to normal pressure to obtain a sintered block.

[0017] Further, in step (S3), in the acid-containing electrolyte, the acid concentration is 0.01-1 wt%, and the acid is at least one selected from the group consisting of phosphoric acid, nitric acid, hydrochloric acid, boric acid, citric acid, and malic acid; the electrolyte further contains 20-30 wt% ethylene glycol, and the balance is water; the energizing is carried out at 60-90℃, under the conditions of a current density of 50-100 mA / g and a voltage of 100-150 V for 1-2 h. During the energizing process, a dense oxide film is formed on the surface of the composite block, improving the dielectric constant.

[0018] The niobium-tantalum composite capacitor anode prepared by the preparation process of the application has uniform distribution of niobium and tantalum, and the capacitor made of the anode as the anode material has excellent performance, fully plays the advantages of tantalum capacitors and niobium capacitors, and the stability is improved.

[0019] The second object of the application is to provide a niobium-tantalum composite capacitor, wherein the anode is the niobium-tantalum composite capacitor anode prepared by the above method.

[0020] The niobium-tantalum composite capacitor is prepared by a preparation method comprising the following steps:

[0021] (S4) immersing the niobium-tantalum composite capacitor anode prepared by the above preparation method in a manganese nitrate solution, taking out the film, repeating 3-5 times to form a manganese dioxide cathode, coating graphite and silver paste on the surface of the manganese dioxide cathode, connecting a lead frame, encapsulating with a high-molecular-weight resin, and aging to obtain a niobium-tantalum composite capacitor.

[0022] Further, in step (S4), the concentration of the manganese nitrate solution is 1-3 wt%, and the coating temperature is 180-230℃; the processes of coating graphite and silver paste, connecting lead wire, packaging, and aging are well known in the art. Still further, the packaging uses epoxy resin, and the aging is performed under the conditions of 1-5 V for 1-2 h, 50-60 V for 1-2 h, 50-70℃ for 1-2 h, 100-110℃ for 1-2 h, and then 50-70℃ and 30-40 V for 30-40 h. DETAILED DESCRIPTION

[0023] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application will be further described below in conjunction with specific examples. The examples described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0024] Example 1

[0025] (S1) 7.3 kg of niobium powder with D50 of 31.2 μm and span of 0.57, 1.3 kg of tantalum powder with D50 of 5.3 μm and span of 0.71, and 0.35 kg of binder were ball milled together, the binder was a mixture of polyvinyl alcohol with number average molecular weight of 26,000 and polyethylene glycol with number average molecular weight of 2,200 in a mass ratio of 6:1, the ball milling process was a ball-to-material ratio of 8:1, a rotation speed of 250 rpm, a ball milling time of 3 h, and a ball milling medium of zirconium oxide with a diameter of 5 mm, and after ball milling, the niobium-tantalum mixed powder was obtained, with D50 of 17.3 μm and span of 0.93;

[0026] (S2) The niobium-tantalum mixed powder was pressed into a compact (3 mm x 2.5 mm x 1.5 mm) with a tantalum wire lead-out wire, and the compact density was 7.1 g / cm 3 , under a vacuum condition of 1 x 10 -3 Pa, pre-sintering at 1350℃ for 0.5 h, then sintering at 1900℃ for 1.5 h,

[0027] cooling to room temperature and returning to normal pressure, to obtain a sintered block;

[0028] (S3) The sintered block was energized in an electrolyte containing 0.1 wt% of phosphoric acid, 0.01 wt% of hydrochloric acid, 22 wt% of ethylene glycol, and the rest being water, under the conditions of 80℃, a current density of 50 mA / g, and a voltage of 130 V for 2 h, to form a dense oxide film on the surface of the sintered block, to obtain a niobium-tantalum composite capacitor anode.

[0029] (S4) Nb-Ta composite capacitor anode was immersed in 2wt% manganese nitrate solution, taken out and coated in a coater at 200°C, repeated 3 times to form manganese oxide film on the surface of Nb-Ta composite capacitor anode, then coated with graphite and silver paste to form cathode, lead out cathode lead, connect lead frame, encapsulate with epoxy resin, and aged under the following conditions: 5V for 1h, increased to 60V for 1h, increased to 60°C for 1h, increased to 110°C for 1h, decreased to 40°C, decreased to 40V for 40h.

[0030] Example 2

[0031] (S1) 8kg of Nb powder with D50 of 31.2μm and span of 0.57, 1kg of Ta powder with D50 of 5.3μm and span of 0.71, and 0.40kg of binder were ball milled, the binder was a mixture of polyvinyl alcohol with number average molecular weight of 26000 and polyethylene glycol with number average molecular weight of 2200 in a mass ratio of 5:1, the ball milling process was ball to material ratio of 8:1, rotation speed of 250rpm, ball milling time of 3h, and ball milling medium was zirconium oxide with diameter of 5mm, after ball milling, the Nb-Ta mixed powder was obtained, with D50 of 17.1μm and span of 0.96;

[0032] Steps (S2), (S3), (S4) were the same as Example 1.

[0033] Example 3

[0034] (S1) 6kg of Nb powder with D50 of 31.2μm and span of 0.57, 1.5kg of Ta powder with D50 of 5.3μm and span of 0.71, and 0.32kg of binder were ball milled, the binder was a mixture of polyvinyl alcohol with number average molecular weight of 26000 and polyethylene glycol with number average molecular weight of 2200 in a mass ratio of 7:1, the ball milling process was ball to material ratio of 8:1, rotation speed of 250rpm, ball milling time of 3h, and ball milling medium was zirconium oxide with diameter of 5mm, after ball milling, the Nb-Ta mixed powder was obtained, with D50 of 16.4μm and span of 1.05;

[0035] Steps (S2), (S3), (S4) were the same as Example 1.

[0036] Example 4

[0037] (S1) 7.3 kg of niobium powder having a D50 of 31.2 μm and a span of 0.57, and 0.3 kg of polyvinyl alcohol having a number average molecular weight of 26,000 were ball milled for 1 h at a ball to material ratio of 8:1, with zirconium oxide having a diameter of 5 mm as the ball milling medium, and a rotation speed of 350 rpm. After stopping the ball milling, 1.3 kg of tantalum powder having a D50 of 5.3 μm and a span of 0.71, and 0.5 kg of polyethylene glycol having a number average molecular weight of 2,200 were added, and ball milling was continued for 2 h at a rotation speed of 200 rpm, to obtain a niobium-tantalum mixed powder having a D50 of 17.2 μm and a span of 0.86.

[0038] Steps (S2), (S3), and (S4) were the same as in Example 1.

[0039] Example 5

[0040] The other conditions were the same as in Example 1, except that in step (S1), the binder was a mixture of polyvinyl alcohol having a number average molecular weight of 30,000 and polyethylene glycol having a number average molecular weight of 1,600 at a mass ratio of 5:1.

[0041] Example 6

[0042] The other conditions were the same as in Example 1, except that in step (S1), the binder was a mixture of polyvinyl alcohol having a number average molecular weight of 20,000 and polyethylene glycol having a number average molecular weight of 3,000 at a mass ratio of 5:1.

[0043] Example 7

[0044] The other conditions were the same as in Example 1, except that in step (S1), the binder was a mixture of polyvinyl alcohol having a number average molecular weight of 10,000 and polyethylene glycol having a number average molecular weight of 2,200 at a mass ratio of 5:1.

[0045] Example 8

[0046] The other conditions were the same as in Example 1, except that in step (S1), the binder was a mixture of polyvinyl alcohol having a number average molecular weight of 50,000 and polyethylene glycol having a number average molecular weight of 2,200 at a mass ratio of 5:1.

[0047] Comparative Example 1

[0048] The other conditions were the same as in Example 1, except that in step (S1), the binder was polyvinyl alcohol having a number average molecular weight of 26,000.

[0049] Comparative Example 2

[0050] The other conditions were the same as in Example 1, except that in step (S1), the binder was polyethylene glycol having a number average molecular weight of 2,200.

[0051] Comparative Example 3

[0052] Other conditions are the same as in Example 1, except that in step (S1), the D50 of the tantalum powder is 25.8 μm, and the span Span = 0.64.

[0053] Comparative Example 4

[0054] Other conditions are the same as in Example 1, except that in step (S1), the D50 of the niobium powder is 8.4 μm, and the span Span = 0.75.

[0055] Application Example

[0056] The capacitors prepared in the above examples were tested for performance, and the results are shown in Table 1 below.

[0057] Table 1: Capacitor performance test results

[0058]

[0059]

[0060] From the data in Table 1, it can be seen that the niobium-tantalum composite capacitor prepared by the process of the present application has the advantages of both niobium capacitors and tantalum capacitors. The reason for the excellent performance of the composite capacitor obtained by the present application is that the niobium and tantalum are more uniformly dispersed by the specific process. Specifically, by using tantalum powder and niobium powder of different particle sizes, and by compounding high-molecular-weight polyvinyl alcohol and low-molecular-weight polyethylene glycol, a niobium-tantalum composite capacitor with excellent comprehensive performance is obtained. In a preferred embodiment of the present application, by using a segmented ball mill, first a high-speed ball milling of large-particle-size niobium powder and polyvinyl alcohol is performed, then small-particle-size tantalum powder and polyethylene glycol are added, and a low-speed ball milling is performed, and finally a capacitor with the best performance can be obtained.

Claims

1. A method for preparing a niobium-tantalum composite capacitor anode, characterized by, The method comprises the following steps: (S1) ball milling niobium powder with D50 of 25-35 μm and span ≤0.8, tantalum powder with D50 of 4-7 μm and span ≤0.8, and a binder to obtain niobium-tantalum mixed powder, wherein the binder is a mixture of polyvinyl alcohol and polyethylene glycol; (S2) pressing the niobium-tantalum mixed powder into a compact with a tantalum wire lead, and vacuum sintering to obtain a sintered compact; (S3) energizing the sintered compact in an acid-containing electrolyte to obtain a niobium-tantalum composite capacitor anode.

2. The production method according to claim 1, characterized by, In step (S1), the number average molecular weight of the polyvinyl alcohol is 20-30 thousand, and the number average molecular weight of the polyethylene glycol is 1600-3000.

3. The preparation method according to claim 1, characterized in that, In step (S1), the mass ratio of the niobium powder, the tantalum powder and the binder is 70-80:10-15:3.2-4.7; and the binder is a mixture of polyvinyl alcohol and polyethylene glycol in a mass ratio of 5-7:

1.

4. The production method according to claim 3, characterized by, In step (S1), the mass ratio of the niobium powder to the tantalum powder is less than 6:

1.

5. The preparation method according to claim 1, characterized in that, In step (S1), the ball-to-material ratio of the ball milling is 5-8:1, the rotation speed is 150-400 rpm, the ball milling time is 3-4 h, the ball medium is zirconium oxide, and the diameter of the ball medium is 4-6 mm.

6. The method of claim 1, wherein, In step (S1), the ball milling is stepwise ball milling, wherein the niobium powder and the polyvinyl alcohol are first added and subjected to high-speed ball milling at a rotation speed of 300-400 rpm for 1-2 h, then the tantalum powder and the polyethylene glycol are added, the rotation speed is reduced to 150-200 rpm, and the ball milling is continued for 2-3 h.

7. The preparation method according to claim 1, characterized in that, The density of the compact in step (S2) is controlled to be 6.8-7.5 g / cm 3 ; the vacuum sintering is pre-sintering at 1 x 10 -3 to 1 x 10 -2 Pa for 0.5-1 h at 1300-1500 °C, then sintering at 1800-2000 °C for 1-2 h, then cooling to room temperature and recovering to normal pressure to obtain a sintered block.

8. The method of claim 1, wherein, In step (S3), in the acid-containing electrolyte, the acid concentration is 0.01-1 wt%, and the acid is at least one selected from the group consisting of phosphoric acid, nitric acid, hydrochloric acid, boric acid, citric acid and malic acid; the electrolyte further contains 20-30 wt% ethylene glycol, and the balance is water.

9. The method of claim 1, wherein, In step (S3), the energizing is performed at 60-90 ℃, a current density of 50-100 mA / g, and a voltage of 100-150 V for 1-2 h.

10. A niobium-tantalum composite capacitor, wherein the anode is the niobium-tantalum composite capacitor anode prepared by the preparation method of any one of claims 1-8.

11. The method for preparing the niobium-tantalum composite capacitor according to claim 10, characterized in that, The method comprises the following steps: (S4) immersing the niobium-tantalum composite capacitor anode prepared by the preparation method of any one of claims 1-8 in a manganese nitrate solution, taking out the coating, repeating the operation for 3-5 times, forming a manganese dioxide cathode, coating graphite and silver paste on the surface of the manganese dioxide cathode, connecting a lead frame, encapsulating with a polymer resin, and aging to obtain a niobium-tantalum composite capacitor.

12. The method of claim 11, wherein, In step (S4), the concentration of the manganese nitrate solution is 1-3 wt%, and the coating temperature is 180-230 ℃.

Images