Anode for a foil tantalum electrolytic capacitor with ultra-high capacitance density and method of manufacture

Abstract

The application discloses a foil type tantalum electrolytic capacitor anode with super high capacitance density and a preparation method thereof. The energy source is a pulse direct current power supply, the pre-processed tantalum foil is used as the anode, the graphite electrode or inert metal is used as the cathode, the anode and the cathode are connected with the pulse direct current power supply, and are placed in an etching solution to perform electrochemical etching. The etching foil is subjected to anodic oxidation in a phosphoric acid aqueous solution to obtain the etched tantalum foil. The electrochemical etching process truly realizes the preparation of the high specific capacity etched tantalum anode foil. For the anode foil with a voltage resistance of 8.3V, the specific capacity is up to 570nF / mm 2 , and the thickness is less than 30μm, which is only 1 / 10 of the traditional sintered tantalum capacitor. If the tantalum capacitor is packaged in a sheet type, the size can be even reduced to below 100μm, which can almost meet the requirements of the most stringent embedded capacitor in technology. If the tantalum capacitor is packaged in a winding type, the maximum capacity can fully meet the requirements of more than 90% of the power system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of tantalum electrolytic capacitor preparation of electronic components, and particularly relates to a foil type tantalum electrolytic capacitor anode with super high capacitance density and a preparation method thereof. BACKGROUND

[0002] Tantalum electrolytic capacitors have become a kind of electronic components that cannot be replaced in harsh environments due to their advantages of high specific capacity, small size, high reliability and good frequency characteristics. At the same time, the disadvantages of tantalum capacitors are also very obvious, which are as follows. Firstly, the price is expensive. The cost of tantalum electrolytic capacitors is closely related to the complex manufacturing process of the anode block in addition to the tantalum material itself. Secondly, although the capacitance density of tantalum capacitors is much higher than that of aluminum electrolytic capacitors, due to the limitation of sintering process, the size of the anode block cannot be further increased, which leads to the limitation of the capacity of tantalum capacitors, and they cannot be widely used in the field of power electronics like aluminum electrolytic capacitors.

[0003] In fact, if etched tantalum foil is used as the anode of tantalum electrolytic capacitor, all problems can be solved. On the one hand, the preparation of etched foil only needs to go through electrochemical etching, and the process is very simple, which can greatly reduce the production cost of tantalum capacitors. In addition, the packaging method of foil type capacitor is generally winding type, which can prepare very large volume capacitors, which also solves the problem of small capacity of tantalum capacitors.

[0004] However, tantalum has extremely stable chemical properties at room temperature and can resist corrosion of almost all acids except hydrofluoric acid. More importantly, even the etchant that can etch tantalum may not necessarily increase its specific surface area. Therefore, although some research on electrochemical etching of tantalum has been conducted since the 1950s, the etching ratio (specific capacity after etching / specific capacity before etching) of tantalum foil has never been reported to exceed 15. Therefore, some scholars turned to niobium foil which is relatively easy to etch, but the specific surface area of niobium etched foil reported so far has only increased by 30 times. Obviously, such small capacitance density cannot meet the actual requirements of foil capacitors. Therefore, it is necessary to propose a new electrochemical etching process to realize the preparation of tantalum capacitor anode with super high capacitance density. SUMMARY

[0005] In order to solve the problems in the prior art, the purpose of the present application is to provide a foil type tantalum electrolytic capacitor anode with super high capacitance density and a preparation method thereof, which can increase the etching ratio, prepare tantalum capacitor anode with super high capacitance density, and reduce the production cost of tantalum capacitors and expand their application range.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A method for preparing a foil type tantalum electrolytic capacitor anode with super high capacitance density, comprising the following steps:

[0008] An electrochemical etching is performed on the pretreated tantalum foil by using a pulse direct current power as an energy source, a graphite electrode or an inert metal as a cathode, and the anode and the cathode being connected with the pulse direct current power and being placed in an etching solution.

[0009] The etched foil is subjected to anodic oxidation in a phosphoric acid aqueous solution to obtain the etched tantalum foil.

[0010] Further, the tantalum foil is pretreated by the following process: the high-purity tantalum foil with a thickness of 20-200 microns is cut, ultrasonic cleaned, dried, and then chemically polished in a mixed acid of hydrofluoric acid and HNO3, and dried.

[0011] Further, the volume ratio of the hydrofluoric acid and HNO3 is 20:55, and the polishing time is 30-120 seconds.

[0012] Further, the etching solution is a methanol solution of 0.01-0.04 mol / L bromide salt.

[0013] Further, the bromide salt is potassium bromide, sodium bromide, ammonium bromide, tetraethylammonium bromide or sodium bromoacetate.

[0014] Further, the pulse direct current power has a current density of 10-30 mA / cm 2 , a frequency of 20-100 Hz, a duty cycle of 20%-40%, and an electrochemical etching time of 10-40 minutes.

[0015] Further, the phosphoric acid aqueous solution has a mass concentration of 0.01%-0.1%.

[0016] Further, the anodic oxidation has a current density of 1-5 mA / cm 2 , a voltage of 3-100 V, and a temperature of 80-90 DEG C.

[0017] A foil type tantalum electrolytic capacitor anode with super high capacitance density prepared by the method has a thickness of less than 200 microns and a capacitance density of 570 nF / mm 2 at a voltage of 8.3 V.

[0018] Compared with the prior art, the method has the following beneficial effects:

[0019] From the product performance, the electrochemical etching process truly realizes the preparation of the high specific capacity etched tantalum anode foil. The CV value is an important index for evaluating the comprehensive performance of the capacitor, and the CV value is more than 5 times that of the tantalum anode prepared by the existing etching technology. For the anode foil with a voltage of 8.3 V, the specific capacity is as high as 570 nF / mm2 The thickness of the tantalum foil is less than 30 microns, only 1 / 10 of the traditional sintered tantalum capacitor. If packaged in a sheet, the size can be reduced to less than 100 microns, almost meeting the requirements of the most stringent embedded capacitor in technology. If packaged in a winding type, the maximum capacity can fully meet the needs of more than 90% of the power system.

[0020] From the production cost, the direct current pulse etching technology used in the application has the advantages of simple operation, low equipment price and good repeatability. Avoid the traditional cumbersome sintering process, also do not need to buy expensive sintering equipment, greatly save the production cost. More importantly, the production line for producing etching foil can be directly used to produce etching tantalum foil by slight improvement, which saves a lot of manpower and financial resources for the development of new projects of enterprises.

[0021] From the technical advantages, the tantalum foil in the application is realized in the mixed acid chemical polishing, which can remove the rough rolling marks on the surface and form a more uniform passivation film. The benefits of this are that the high-energy area on the surface of the tantalum foil is eliminated, the pores on the surface of the tantalum foil are more uniform, which is beneficial to reduce "pore merging" and increase the specific capacity.

[0022] Further, the application uses direct current pulse as the energy source, and the pulse current has three advantages. First, it can increase the pore probability of the surface, increase the pore density, and increase the specific capacity; second, it can weaken the polarization state of the tantalum foil, slow down the corrosion of the tantalum foil, effectively reduce "pore merging", and increase the specific capacity; third, it can increase the adsorption of oxygen on the pore wall in the zero current time, slow down the etching of the "wall" of the corrosion pit, and is beneficial to increase the depth of the corrosion hole, and further improve the specific capacity.

[0023] Further, the etchant of the application is limited to bromide salt, and fluorine salt and chlorine are more likely to obtain high specific capacity. The application compares the etching effect after using NH4F, NaBr and NaCl as etchant.

[0024] The specific capacity of the tantalum anode foil prepared by the application is the highest in the same type of work, and the CV value is also the highest in the same type of work, which effectively promotes the application of tantalum electrolytic capacitor in more rich scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The cross-sectional view of the etching foil obtained in Example 5.

[0026] Figure 2The micrographs of etched tantalum foils with and without chemical polishing, wherein (a) is the micrograph of etched tantalum foil without chemical polishing, (b) is the partial enlarged view of the box in (a); (c) is the micrograph of etched tantalum foil after chemical polishing, and (d) is the partial enlarged view of the box in (c).

[0027] Figure 3 The micrographs of etched tantalum foils with and without chemical polishing, wherein (a) is the micrograph of etched tantalum foil without chemical polishing, (b) is the partial enlarged view of the box in (a); (c) is the micrograph of etched tantalum foil after chemical polishing, and (d) is the partial enlarged view of the box in (c).

[0028] Figure 4 The micrographs of etched tantalum foils with and without chemical polishing, wherein (a) is the micrograph of etched tantalum foil without chemical polishing, (b) is the partial enlarged view of the box in (a); (c) is the micrograph of etched tantalum foil after chemical polishing, and (d) is the partial enlarged view of the box in (c). DETAILED DESCRIPTION

[0029] The present application will be described in detail by the following examples.

[0030] The preparation method of the foil tantalum electrolytic capacitor anode with super-high capacitance density comprises the following steps:

[0031] Step one: cut the high-purity tantalum foil with a thickness of 20-200 μm into the required size, and clean it in deionized water, anhydrous ethanol and acetone successively, and dry it in a vacuum oven. The cleaned tantalum foil is chemically polished in a mixed acid of hydrofluoric acid and HNO3 with a volume ratio of 20:55 for 30-120 s, and dried in an oven for standby;

[0032] Step two: add bromide salt into methanol solvent, and stir until uniform to obtain a corrosion solution with a concentration of 0.01-0.04 mol / L; the bromide salt is potassium bromide, sodium bromide or ammonium bromide, etc., and the bromide salt is a bromo-organic salt (tetraethylammonium bromide or sodium bromoacetate, etc.).

[0033] Step three: take a pulse direct current power supply as an energy source, take the tantalum foil as an anode, and take graphite electrode or inert metal as a cathode, both of which are connected with the pulse direct current power supply, and place them in the corrosion solution to perform electrochemical corrosion.

[0034] The current density of the pulse direct current power supply is 10-30 mA / cm 2 (preferably 15 mA / cm 2 ), the frequency is 20-100 Hz, the duty cycle is 20%-40%, and the electrochemical corrosion time is 10-40 min.

[0035] Step four: the obtained etching foil is subjected to anodic oxidation in a dilute phosphoric acid aqueous solution with a mass concentration of 0.01%-0.1% to obtain a corrosion tantalum foil, that is, a foil type electrolytic capacitor anode with super-high capacitance density. In the anodic oxidation, the current density is 1-5 mA / cm 2 , the voltage is 3-100 V, and the temperature is 80-90 DEG C. The anodic oxidation time is the time required for the current density to decrease to less than 50 uA / cm 2 after reaching the energizing voltage.

[0036] The anodic oxidation time is the time required for the current density to decrease to less than 50 uA / cm 2 after reaching the anodic oxidation voltage. With the increase of the energizing voltage, the oxide film gradually becomes thicker, and the metal foil changes from a conductor to an insulator covered with an oxide film. At this time, the current flowing through the anode sheet is very small. If the anodic oxidation time is long enough, the current can finally reach the nA level.

[0037] The present application first uses a direct current pulse as a power source in an electrochemical etching process to prepare a super-thin tantalum electrolytic capacitor anode with super-high capacitance density. The specific surface area of the corrosion tantalum foil is increased by 63 times, the thickness is only 30 mu m, and the capacitance density can reach 570 nF / mm 2 after energizing under a voltage of 8.3 V.

[0038] Example 1

[0039] Step one: a tantalum foil with a thickness of 30 mu m is cut into a square with a size of 1 cm 2 , and is sequentially ultrasonically cleaned in deionized water, anhydrous ethanol and acetone for 10 min, and is dried in a vacuum oven at 120 DEG C. The cleaned tantalum foil is chemically polished in a mixed acid of hydrofluoric acid and HNO3 with a volume ratio of 20:55, the polishing time is 30 s, and the tantalum foil is dried in an oven for standby;

[0040] Step two: sodium bromide is added to a methanol solvent and stirred until uniform to obtain a corrosion solution with a concentration of 0.01 mol / L;

[0041] Step three: a pulse direct current power source is used as an energy source, a tantalum foil is used as an anode, and a graphite electrode or an inert metal is used as a cathode. The anode and the cathode are connected with the pulse direct current power source and are placed in the corrosion solution to perform electrochemical corrosion, and a corrosion tantalum foil is obtained. In the pulse direct current power source, the current density is 10 mA / cm 2 , the frequency is 20 Hz, the duty cycle is 20%, and the electrochemical corrosion time is 10 min.

[0042] Step four: the obtained etching foil is subjected to anodic oxidation in a dilute phosphoric acid aqueous solution with a mass concentration of 0.01%-0.1% to obtain a corrosion tantalum foil, that is, a foil type electrolytic capacitor anode with super-high capacitance density. In the anodic oxidation, the current density is 1-5 mA / cm 2, the voltage is 3V, and the temperature is 80℃, to obtain a foil type electrolytic capacitor anode with super-high capacitance density.

[0043] Example 2

[0044] Step one: cut the tantalum foil with a thickness of 30μm into 1cm 2 sized square blocks, and then ultrasonic cleaning in deionized water, anhydrous ethanol and acetone for 10min, and drying in a vacuum oven at 120℃. The cleaned tantalum foil is chemically polished in a mixed acid of hydrofluoric acid-HNO3 with a volume ratio of 20:55 for 60s, and dried in an oven for standby;

[0045] Step two: add potassium bromide into a methanol solvent, stir until mixed evenly, to obtain a corrosion solution with a concentration of 0.02mol / L;

[0046] Step three: take a pulse direct current power as an energy source, take the tantalum foil as an anode, and take a graphite electrode or inert metal as a cathode, both the anode and the cathode are connected with the pulse direct current power, and are placed in the corrosion solution to perform electrochemical corrosion, to obtain a corroded tantalum foil, wherein the current density of the pulse direct current power is 15mA / cm 2 , the frequency is 30Hz, the duty cycle is 30%, and the electrochemical corrosion time is 10min.

[0047] Step four: anodize the obtained etched foil in a 0.01wt% phosphoric acid aqueous solution for 1h, the current density of anodization is 1mA / cm 2 , the voltage is 5V, and the temperature is 85℃, to obtain a foil type electrolytic capacitor anode with super-high capacitance density.

[0048] Example 3

[0049] Step one: cut the tantalum foil with a thickness of 30μm into 1cm 2 sized square blocks, and then ultrasonic cleaning in deionized water, anhydrous ethanol and acetone for 10min, and drying in a vacuum oven at 120℃. The cleaned tantalum foil is chemically polished in a mixed acid of hydrofluoric acid-HNO3 with a volume ratio of 20:55 for 90s, and dried in an oven for standby;

[0050] Step two: add ammonium bromide into a methanol solvent, stir until mixed evenly, to obtain a corrosion solution with a concentration of 0.03mol / L;

[0051] Step three: take a pulse direct current power as an energy source, take the tantalum foil as an anode, and take a graphite electrode or inert metal as a cathode, both the anode and the cathode are connected with the pulse direct current power, and are placed in the corrosion solution to perform electrochemical corrosion, to obtain a corroded tantalum foil, wherein the current density of the pulse direct current power is 20mA / cm 2, the frequency is 50Hz, the duty cycle is 30%, and the electrochemical corrosion time is 10 minutes.

[0052] Step four: the obtained etching foil is anodized in 0.01wt% phosphoric acid aqueous solution, the current density of anodization is 1mA / cm 2 , the voltage is 20V, and the temperature is 90℃, to obtain a foil type electrolytic capacitor anode with super-high capacitance density.

[0053] Example 4

[0054] Step one: cut the tantalum foil with a thickness of 30μm into 1cm 2 sized square blocks, and then ultrasonic clean them in deionized water, anhydrous ethanol and acetone for 10 minutes, and dry them in a vacuum oven at 120℃. Clean the tantalum foil in a mixed acid of hydrofluoric acid and HNO3 with a volume ratio of 20:55, polish for 120s, and dry in an oven for standby;

[0055] Step two: add sodium bromide to a methanol solvent, stir until mixed evenly, and obtain a corrosion solution with a concentration of 0.04mol / L;

[0056] Step three: use a pulse direct current power supply as an energy source, use a tantalum foil as an anode, and use a graphite electrode or an inert metal as a cathode, both the anode and the cathode are connected to the pulse direct current power supply, and are placed in the corrosion solution to perform electrochemical corrosion, to obtain a corroded tantalum foil, wherein the current density of the pulse direct current power supply is 30mA / cm 2 , the frequency is 100Hz, the duty cycle is 40%, and the electrochemical corrosion time is 10 minutes.

[0057] Step four: the obtained etching foil is anodized in 0.01wt% phosphoric acid aqueous solution, the current density of anodization is 1mA / cm 2 , the voltage is 5V, and the temperature is 80℃, to obtain a foil type electrolytic capacitor anode with super-high capacitance density.

[0058] Example 5

[0059] Step one: cut the tantalum foil with a thickness of 30μm into 1cm 2 sized square blocks, and then ultrasonic clean them in deionized water, anhydrous ethanol and acetone for 10 minutes, and dry them in a vacuum oven at 120℃. Clean the tantalum foil in a mixed acid of hydrofluoric acid and HNO3 with a volume ratio of 20:55, polish for 90s, and dry in an oven for standby;

[0060] Step two: add sodium bromide to a methanol solvent, stir until mixed evenly, and obtain a corrosion solution with a concentration of 0.02mol / L;

[0061] Step three: using a pulse direct current power supply as an energy source, using tantalum foil as an anode, and using a graphite electrode or inert metal as a cathode, the anode and the cathode are connected with the pulse direct current power supply and placed in the etching solution to perform electrochemical etching, and an etched tantalum foil is obtained, wherein the current density of the pulse direct current power supply is 15 mA / cm 2 , the frequency is 50 Hz, the duty cycle is 30%, and the electrochemical etching time is 20 min.

[0062] Step four: the obtained etched foil is anodized in a 0.01wt% phosphoric acid aqueous solution, the current density of anodization is 1 mA / cm 2 , the voltage is 8 V, and the temperature is 85℃, and a foil type electrolytic capacitor anode with super-high capacitance density is obtained.

[0063] Example 6

[0064] Step one: cut the tantalum foil with a thickness of 30μm into 1cm 2 sized square blocks, ultrasonic clean them in deionized water, anhydrous ethanol and acetone for 10 min, and dry them in a vacuum oven at 120℃. The cleaned tantalum foil is chemically polished in a mixed acid of hydrofluoric acid-HNO3 with a volume ratio of 20:55, the polishing time is 60s, and the tantalum foil is dried in an oven for standby;

[0065] Step two: add bromoethylammonium into a methanol solvent, stir until uniform, and obtain a concentration of 0.02mol / L etching solution;

[0066] Step three: using a pulse direct current power supply as an energy source, using tantalum foil as an anode, and using a graphite electrode or inert metal as a cathode, the anode and the cathode are connected with the pulse direct current power supply and placed in the etching solution to perform electrochemical etching, and an etched tantalum foil is obtained, wherein the current density of the pulse direct current power supply is 20 mA / cm 2 , the frequency is 30 Hz, the duty cycle is 40%, and the electrochemical etching time is 30 min.

[0067] Step four: the obtained etched foil is anodized in a 0.01wt% phosphoric acid aqueous solution, the current density of anodization is 5 mA / cm 2 , the voltage is 30 V, and the temperature is 90℃, and a foil type electrolytic capacitor anode with super-high capacitance density is obtained.

[0068] Example 7

[0069] Step one: cut the tantalum foil with a thickness of 30μm into 1cm 2The cleaned tantalum foil is chemically polished in a mixed acid of hydrofluoric acid and HNO3 with a volume ratio of 20:55 for 120 s, and dried in an oven for standby;

[0070] Step two: sodium bromoacetate is added to a methanol solvent and stirred until mixed evenly to obtain a corrosion solution with a concentration of 0.01 mol / L;

[0071] Step three: a pulse direct current power source is used as an energy source, a tantalum foil is used as an anode, and a graphite electrode or an inert metal is used as a cathode, both the anode and the cathode are connected to the pulse direct current power source, and are placed in the corrosion solution to perform electrochemical corrosion, thereby obtaining an etched tantalum foil, wherein the current density of the pulse direct current power source is 30 mA / cm 2 , the frequency is 50 Hz, the duty cycle is 20%, and the electrochemical corrosion time is 40 min.

[0072] Step four: the obtained etched foil is anodized in a 0.01wt% phosphoric acid aqueous solution, the current density of anodization is 3 mA / cm 2 , the voltage is 50 V, and the temperature is 85°C, thereby obtaining a foil type electrolytic capacitor anode with ultra-high capacitance density.

[0073] Example 8

[0074] Step one: a tantalum foil with a thickness of 30 μm is cut into a square with a size of 1 cm 2 , and is sequentially ultrasonically cleaned in deionized water, anhydrous ethanol, and acetone for 10 min, and dried in a vacuum oven at 120°C. The cleaned tantalum foil is chemically polished in a mixed acid of hydrofluoric acid and HNO3 with a volume ratio of 20:55 for 90 s, and dried in an oven for standby;

[0075] Step two: sodium bromoacetate is added to a methanol solvent and stirred until mixed evenly to obtain a corrosion solution with a concentration of 0.02 mol / L;

[0076] Step three: a pulse direct current power source is used as an energy source, a tantalum foil is used as an anode, and a graphite electrode or an inert metal is used as a cathode, both the anode and the cathode are connected to the pulse direct current power source, and are placed in the corrosion solution to perform electrochemical corrosion, thereby obtaining an etched tantalum foil, wherein the current density of the pulse direct current power source is 15 mA / cm 2 , the frequency is 30 Hz, the duty cycle is 30%, and the electrochemical corrosion time is 30 min.

[0077] Step four: the obtained etched foil is anodized in a 0.01wt% phosphoric acid aqueous solution, the current density of anodization is 5 mA / cm 2, the voltage is 100V, and the temperature is 85℃, to obtain a foil type electrolytic capacitor anode with super-high capacitance density.

[0078] Example 9

[0079] Step one: cut the tantalum foil with a thickness of 30μm into 1cm 2 sized blocks, and then ultrasonic clean them in deionized water, anhydrous ethanol and acetone for 10min, and dry them in a vacuum oven at 120℃. Clean the tantalum foil and then chemical polish it in a mixed acid of hydrofluoric acid and HNO3 with a volume ratio of 20:55 for 90s, and dry it in an oven for standby;

[0080] Step two: add bromoethylammonium into a methanol solvent, and stir until it is uniformly mixed to obtain a corrosion solution with a concentration of 0.03mol / L;

[0081] Step three: use a pulse direct current power supply as an energy source, use the tantalum foil as an anode, and use a graphite electrode or an inert metal as a cathode, both the anode and the cathode are connected with the pulse direct current power supply, and then place them in the corrosion solution to perform electrochemical corrosion, to obtain a corroded tantalum foil, wherein the current density of the pulse direct current power supply is 20mA / cm 2 , the frequency is 60Hz, the duty cycle is 20%, and the electrochemical corrosion time is 40min.

[0082] Step four: anodize the obtained etched foil in a 0.01wt% phosphoric acid aqueous solution, the current density of the anodization is 2mA / cm 2 , the voltage is 10V, and the temperature is 85℃, to obtain a foil type electrolytic capacitor anode with super-high capacitance density.

[0083] Example 10

[0084] Step one: cut the tantalum foil with a thickness of 30μm into 1cm 2 sized blocks, and then ultrasonic clean them in deionized water, anhydrous ethanol and acetone for 10min, and dry them in a vacuum oven at 120℃. Clean the tantalum foil and then chemical polish it in a mixed acid of hydrofluoric acid and HNO3 with a volume ratio of 20:55 for 120s, and dry it in an oven for standby;

[0085] Step two: add sodium bromide into a methanol solvent, and stir until it is uniformly mixed to obtain a corrosion solution with a concentration of 0.04mol / L;

[0086] Step three: use a pulse direct current power supply as an energy source, use the tantalum foil as an anode, and use a graphite electrode or an inert metal as a cathode, both the anode and the cathode are connected with the pulse direct current power supply, and then place them in the corrosion solution to perform electrochemical corrosion, to obtain a corroded tantalum foil, wherein the current density of the pulse direct current power supply is 20mA / cm 2, the frequency is 100 Hz, the duty cycle is 20%, and the electrochemical corrosion time is 40 min.

[0087] Step four: the obtained etching foil is anodized in 0.01wt% phosphoric acid solution, the current density of anodization is 2mA / cm 2 , the voltage is 10V, and the temperature is 85℃, to obtain a foil type electrolytic capacitor anode with super high capacitance density.

[0088] The performance test results of examples 1-10 are shown in table 1.

[0089] Table 1: capacity test results of examples 1-10

[0090]

[0091] As can be seen from table 1, the foil type tantalum electrolytic capacitor anode with super high capacitance density and the preparation method thereof provided by example 5 of the present application have achieved very ideal technical effects, breaking through the bottleneck of tantalum material being difficult to etch by electrochemical method for many years. Figure 1 and Figure 3 The thickness of the etched tantalum foil is only less than 30μm, and even after anodization under a voltage of 3V-100V, the total thickness is only increased by 6-200nm; from the specific capacity and micro-morphology, the etch pit radius of the etched foil is between 1-2μm, and the specific capacity is as high as 756μF / cm 2 , and after energization at a voltage of 8V, the specific capacity is still 570nF / mm 2 .

[0092] The specific capacity is calculated according to the formula C=εS / d, where ε is the dielectric constant, S is the area, and d is the distance between the two plates of the capacitor. The increase in specific capacity directly reflects the increase in specific surface area. The specific capacity of the flat tantalum foil before etching is 12μF / cm 2 , and the highest specific capacity of the etched tantalum foil is 756μF / cm 2 , which is equivalent to an increase of 63 times in the specific surface area of the Ta foil (etching ratio of 63).

[0093] Example 11

[0094] Step one: cut the tantalum foil with a thickness of 200μm into 1cm 2 sized squares, ultrasonic clean in deionized water, anhydrous ethanol and acetone for 10min, and dry in a vacuum oven at 120℃. Chemically polish the cleaned tantalum foil in a mixed acid of hydrofluoric acid-HNO3 with a volume ratio of 20:55, polish for 50s, and dry in an oven for standby;

[0095] Step two: tetraethylammonium bromide is added to a methanol solvent, stirred until mixed evenly, to obtain a concentration of 0.01 mol / L of the etching solution;

[0096] Step three: a pulse direct current power supply is used as an energy source, a tantalum foil is used as an anode, and a graphite electrode or an inert metal is used as a cathode, the anode and the cathode are both connected with the pulse direct current power supply, and are placed in the etching solution to perform electrochemical etching, to obtain an etched tantalum foil, wherein the current density of the pulse direct current power supply is 30 mA / cm 2 , the frequency is 20 Hz, the duty cycle is 20%, and the electrochemical etching time is 10 min.

[0097] Step four: the obtained etched foil is anodized in a 0.05wt% phosphoric acid aqueous solution, the current density of anodization is 1 mA / cm 2 , the voltage is 60 V, and the temperature is 80℃, to obtain a foil type electrolytic capacitor anode with super-high capacitance density.

[0098] Example 12

[0099] Step one: a tantalum foil with a thickness of 20 μm is cut into a square with a size of 1 cm 2 , and is ultrasonically cleaned in deionized water, anhydrous ethanol and acetone for 10 min, and is dried in a vacuum oven at 120℃. The cleaned tantalum foil is chemically polished in a mixed acid of hydrofluoric acid-HNO3 with a volume ratio of 20:55, the polishing time is 80 s, and the tantalum foil is dried in an oven for standby;

[0100] Step two: ammonium bromide is added to a methanol solvent, stirred until mixed evenly, to obtain a concentration of 0.02 mol / L of the etching solution;

[0101] Step three: a pulse direct current power supply is used as an energy source, a tantalum foil is used as an anode, and a graphite electrode or an inert metal is used as a cathode, the anode and the cathode are both connected with the pulse direct current power supply, and are placed in the etching solution to perform electrochemical etching, to obtain an etched tantalum foil, wherein the current density of the pulse direct current power supply is 10 mA / cm 2 , the frequency is 100 Hz, the duty cycle is 40%, and the electrochemical etching time is 20 min.

[0102] Step four: the obtained etched foil is anodized in a 0.1wt% phosphoric acid aqueous solution, the current density of anodization is 5 mA / cm 2 , the voltage is 3 V, and the temperature is 90℃, to obtain a foil type electrolytic capacitor anode with super-high capacitance density.

[0103] Example 13

[0104] Step one: a tantalum foil with a thickness of 100 μm is cut into a square with a size of 1 cm 2The cleaned tantalum foil is chemically polished in a mixed acid of hydrofluoric acid and HNO3 with a volume ratio of 20:55 for 30 seconds, and is dried in an oven for standby;

[0105] Step two: sodium bromoacetate is added into a methanol solvent and stirred until uniform, to obtain a corrosion liquid with a concentration of 0.03 mol / L;

[0106] Step three: a pulse direct current power supply is used as an energy source, a tantalum foil is used as an anode, and a graphite electrode or an inert metal is used as a cathode; the anode and the cathode are connected with the pulse direct current power supply and are placed in the corrosion liquid to perform electrochemical corrosion, to obtain an etched tantalum foil, wherein the current density of the pulse direct current power supply is 15 mA / cm 2 , the frequency is 50 Hz, the duty cycle is 30%, and the electrochemical corrosion time is 30 min.

[0107] Step four: the obtained etched foil is subjected to anodic oxidation in a 0.01wt% phosphoric acid aqueous solution, the current density of the anodic oxidation is 3 mA / cm 2 , the voltage is 100 V, and the temperature is 83 DEG C, to obtain a foil type electrolytic capacitor anode with an ultra-high capacitance density.

[0108] In terms of product performance, the electrochemical etching process proposed in the application truly realizes the preparation of a high-specific-capacity etched tantalum anode foil. The CV value is an important indicator for evaluating the comprehensive performance of a capacitor. If the CV value is considered, the CV value of the etched tantalum anode prepared by the existing etching technology is more than 5 times that of the existing etching technology. For an anode foil with a withstand voltage of 8.3 V, the specific capacity is as high as 570 nF / mm 2 , and the thickness is less than 30 mu m, which is only 1 / 10 of that of a traditional sintered tantalum capacitor. The effect is shown in Figure 1 If a chip-type package is used, the size can be reduced to less than 100 mu m, which can almost meet the requirements of the most stringent embedded capacitor. If a winding-type package is used, the maximum capacity can fully meet the requirements of more than 90% of power systems.

[0109] In terms of production cost, the direct current pulse etching technology used in the application has the advantages of simple operation, low equipment price and good repeatability. The traditional complicated sintering process is avoided, and expensive sintering equipment does not need to be purchased, which greatly saves the production cost. More importantly, the production line for producing etched foils can be directly used to produce etched tantalum foils after slight improvement, which saves a lot of manpower and financial resources for the development of new projects of enterprises.

[0110] From the technical advantages, the tantalum foil in the application is realized in the mixed acid for chemical polishing, on the one hand, the surface rough rolling marks are removed, and on the other hand, it is beneficial to form a more uniform passivation film. Figure 2 As shown in the figure, the specific capacity after polishing is increased by 54% compared with that before polishing.

[0111] The application uses direct current pulse as an energy source, and the pulse current has three advantages. First, it can increase the pore probability of the surface, improve the pore density and increase the specific capacity; second, it can weaken the polarization state of the tantalum foil, slow down the corrosion of the tantalum foil, effectively reduce the 'pore merging', and increase the specific capacity; third, it can increase the adsorption of oxygen on the pore wall in the zero current time, slow down the etching of the 'wall' of the corrosion pit, and is beneficial to increase the depth of the corrosion hole, and further improve the specific capacity, and the effect is as shown in Figure 3 (a), (b), (c) and (d) in the figure, the specific capacity is 756 μF / cm 2 .

[0112] The etchant of the application is only limited to bromide salt, and the specific capacity is higher than that of fluoride salt and chlorine, and the application compares the etching effect after using NH4F, NaBr and NaCl as etchant, as shown in Figure 4 (a), (b) and (c), it can be seen that the size of the corrosion pit after Cl ion etching is very large, close to 20 μm, which cannot greatly improve the specific surface area of the tantalum foil, and the specific capacity after etching for 5 min is only 34 μF / cm 2 . The size of the etching pit after F ion etching is slightly smaller, about 10 μm, and the specific capacity is 180 μF / cm 2 , although the effect is better than that of Cl ion etching, but still cannot meet the requirements. Looking at the tantalum foil surface after Br ion etching, there are many etching pits uniformly distributed, and the specific capacity is as high as 350 μF / cm 2 .

[0113] The application breaks through the difficulty of tantalum metal in electrochemical processing, and first prepares an ultra-thin tantalum electrolytic capacitor anode with ultra-high capacitance density by a low-cost, simple operation and low-energy-consumption method. Again, the vitality of tantalum capacitor is revived, which will promote the application of tantalum capacitor in more scenes.

Claims

1. A method for preparing the anode of a foil-type tantalum electrolytic capacitor with ultra-high capacitance density, characterized in that, Includes the following steps: Using a pulsed DC power supply as the energy source, a pretreated tantalum foil as the anode, and a graphite electrode or inert metal as the cathode, both the anode and cathode are connected to the pulsed DC power supply and placed in a corrosion solution for electrochemical corrosion. Anodizing the etched foil in an aqueous phosphoric acid solution yields a foil-type tantalum electrolytic capacitor anode with ultra-high capacitance density. The corrosive solution is a methanol solution of bromide salt with a concentration of 0.01-0.04 mol / L. The bromide salt is potassium bromide, sodium bromide, ammonium bromide, tetraethylammonium bromide, or sodium bromoacetate. The pretreatment process for tantalum foil is as follows: high-purity tantalum foil with a thickness of 20-200μm is cut, ultrasonically cleaned, dried, chemically polished in hydrofluoric acid-HNO3 mixed acid, and then dried.

2. The method for preparing the anode of a foil-type tantalum electrolytic capacitor with ultra-high capacitance density according to claim 1, characterized in that, The volume ratio of hydrofluoric acid to HNO3 is 20:55; the polishing time is 30-120s.

3. The method for preparing the anode of a foil-type tantalum electrolytic capacitor with ultra-high capacitance density according to claim 1, characterized in that, The current density of the pulsed DC power supply is 10-30 mA / cm². 2 The frequency is 20-100Hz, the duty cycle is 20%-40%, and the electrochemical corrosion time is 10-40min.

4. The method for preparing the anode of a foil-type tantalum electrolytic capacitor with ultra-high capacitance density according to claim 1, characterized in that, The mass concentration of the phosphoric acid aqueous solution is 0.01%-0.1%.

5. The method for preparing the anode of a foil-type tantalum electrolytic capacitor with ultra-high capacitance density according to claim 1, characterized in that, The current density for anodizing is 1-5 mA / cm². 2 The voltage is 3-100V and the temperature is 80-90℃.

6. An anode of a foil-type tantalum electrolytic capacitor with ultra-high capacitance density prepared by the method according to any one of claims 1-5, characterized in that, The anode thickness is less than 200 μm, and the capacitance density can reach 570 nF / mm² at a withstand voltage of 8.3 V. 2 .

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