Method for improving reliability of dielectric layer of tantalum electrolytic capacitor by gradient boosting

Abstract

The present application relates to the technical field of tantalum electrolytic capacitor manufacturing, and discloses a method for improving the reliability of a tantalum electrolytic capacitor medium layer by gradient voltage boosting, comprising the following steps: fixing a tantalum anode block in a cathode tank body provided with a polytetrafluoroethylene insulating inner frame and injecting electrolyte for circulating flow; controlling the gradually increasing formation voltage provided by an external power supply to deposit a tantalum pentoxide medium layer on the surface of the tantalum anode block; when the formation voltage reaches a high voltage range, the voltage between adjacent voltage steps is adjusted and a constant voltage operation is maintained to introduce an electric field relaxation operation, the electric field topology of the tank body is reshaped, the local overcurrent and solute depletion in the deep part of the porous skeleton under a high voltage state are inhibited, the accumulation of Joule heat is eliminated, the sudden change of the amorphous oxide film to the crystalline state is fundamentally blocked, the leakage current is reduced, and the withstand voltage level of the medium layer is improved.

Description

Technical Field

[0001] This invention relates to the field of tantalum electrolytic capacitor manufacturing technology, and more specifically, to a method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor through gradient voltage boosting. Background Technology

[0002] The uniformity of the dielectric oxide film on the surface of the porous tantalum anode block determines the withstand voltage index of the component. The conventional practice is to place the porous tantalum anode block in an acidic formation mother liquor and use an external field to drive oxygen-containing polar ions to migrate directionally into the depths of the multi-level micropores inside the framework, thereby causing an electrochemical film formation reaction on the effective working surface of the three-dimensional framework to grow a tantalum pentoxide dielectric insulating layer with a specific thickness. Under the conditions of large-scale continuous formation production, the porous tantalum anode block needs to operate continuously in a high-temperature, strong acid, and progressively increasing pressure environment. The existing formation structure often deforms due to insufficient material strength, resulting in fluctuations in the anode-cathode spacing. At the same time, the insulating adhesive layer laid on the sidewall is easily hydrolyzed in the acid and dissolves impurities into the formation mother liquor, deteriorating the conductivity of the mother liquor. In addition, the charged sidewall of the conventional formation tank generates disordered stray currents. The stray current flow lines overlap with the non-directional electric field entering the porous structure, causing the current flow lines to excessively accumulate at the edge defect sites of the porous framework, generating local Joule heating and destroying the stability of the film formation.

[0003] Not only are there limitations at the hardware level, such as the physical boundaries of the formation tank, but the electrical control methods also have shortcomings. For example, Chinese invention patent application CN114360911A discloses a method for preparing a chip solid electrolyte tantalum capacitor. At room temperature, the voltage is over-adjusted to 1.3 times the predetermined activation voltage in one go using constant current or constant power and maintained for a long time, followed by high-temperature constant voltage. This control logic, which relies solely on the high-voltage over-adjustment in the early stage, is prone to irreversible mass transfer depletion and non-directional aggregation of polar ions inside the micropores when facing porous frameworks under high-voltage conditions. This is because the micropores are under high field strength overload for a long time and lack transient bias adjustment at the surface level. This makes it difficult to guide the solute to penetrate evenly into the deepest part of the micropore channels, and instead causes localized damage at the defect sites of the framework. Current accumulation generates Joule heating and disrupts film stability, ultimately leading to crystallization failure when the voltage is increased to a high level. This makes it impossible to guarantee the consistency of the dielectric layer under high voltage conditions. To suppress overcurrent at specific sites, linear adjustment methods such as extending the process time or slowing down the voltage increase rate are only external overall time control and cannot reconstruct the current distribution logic inside the micropores. Because they ignore the causal relationship between polar ion migration and local electric field distortion, simply slowing down the voltage increase rate causes irreversible mass transfer depletion of polar ions inside the channels under the attraction of continuous electric field force. This makes it impossible to build a high-resistivity polarization shielding layer in the defect micro-region in time, ultimately triggering avalanche crystallization failure when the voltage is increased to a high level. This creates an inherent conflict between extending the process cycle and adaptive redistribution of current density inside the channels.

[0004] Therefore, the technical problem to be solved by this invention is how to reshape the physical boundary of the tank through structural optimization to form a directional vertical electric field, and coordinate the composite electrolyte system and the step-up voltage control mechanism to trigger the adaptive distribution of the current density inside the channel, eliminate stray current interference and mass transfer resistance in the high-voltage area, so as to achieve in-situ repair of defect sites. Summary of the Invention

[0005] This invention provides a method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor through gradient voltage boosting, comprising the following steps:

[0006] Step S1: Fix the tantalum anode block into the all-metal integral cathode tank with a detachable glue-free insulating inner frame, and inject the bulk electrolyte containing nitrate ions and phosphate ions. Control the bulk electrolyte to circulate in the all-metal integral cathode tank at a constant flow rate. The detachable glue-free insulating inner frame covers all the inner walls of the all-metal integral cathode tank to block the sidewall conductive channels.

[0007] Step S2, in the main formation stage, a polarization voltage is applied between the all-metal integral cathode tank and the tantalum anode block using an external DC power supply. The formation voltage provided by the external DC power supply is controlled to be progressively increased in a multi-stage progressive voltage step, including a combination of low-voltage constant current boost and high-voltage step boost, so as to deposit an amorphous tantalum pentoxide dielectric layer on the surface of the tantalum anode block.

[0008] Step S3: When the formation voltage reaches the high voltage range of 200V to 300V, an electric field relaxation operation is switched between adjacent voltage steps. Whenever the formation voltage increases by 20V, the external DC power supply is adjusted to reduce the currently applied formation voltage by 5V to 15V to generate the reduced formation voltage. The reduced formation voltage is then maintained at a constant voltage for 1min to 3min, and the multi-stage progressive voltage step is restored.

[0009] Preferably, the mass percentage concentration of nitric acid in the bulk electrolyte is 0.5% to 2.0%, and the mass percentage concentration of phosphoric acid is 10% to 15%; during the main formation stage, the temperature of the bulk electrolyte is 75°C to 85°C; before the start of the main formation stage, the liquid level of the bulk electrolyte in the all-metal integral cathode tank is 15cm to 20cm, and the circulation flow rate is 5L / min to 8L / min.

[0010] Preferably, the multi-stage progressive voltage ladder includes a low-voltage constant current boost stage and a high-voltage step boost stage; in the low-voltage constant current boost stage, the formation voltage is increased from 0V to 150V with constant current, and the constant current density is 2mA / cm² to 5mA / cm²; after the formation voltage reaches 150V, the high-voltage step boost stage is entered, and the formation voltage is increased by 5V increments per stage, and the constant voltage is maintained for 2min to 4min at each stage.

[0011] Preferably, the electric field relaxation operation in step S3 includes the following sub-steps: Step S31, whenever the formation voltage increases by 20V, the external DC power supply is controlled to reduce the currently applied formation voltage by 5V to 15V within 1s to 3s to generate the reduced formation voltage, and a bias potential difference is formed between the surface and interior of the tantalum anode block; Step S32, the ion concentration distribution of the bulk electrolyte is adjusted based on the bias potential difference, and the external DC power supply is kept in a constant voltage state for 1min to 3min under the reduced formation voltage.

[0012] Preferably, after the main formation stage is completed, the following steps are included: Step S4, the tantalum anode block is removed from the bulk electrolyte and washed in flowing deionized water at a temperature of 80°C to 90°C for 30 min to 40 min; Step S5, the washed tantalum anode block is dried in an environment at a temperature of 105°C to 115°C for 45 min to 60 min and the dried tantalum anode block is obtained.

[0013] Preferably, in step S1, the detachable glue-free insulating inner frame is made of polytetrafluoroethylene and covers the inner wall of the all-metal integral cathode tank. The vertical distance between the detachable glue-free insulating inner frame and the bottom of the all-metal integral cathode tank is 2cm to 3cm.

[0014] Preferably, the main formation stage in step S2 includes a film thickness monitoring step, which includes the following sub-steps: Step S21, in the main formation stage, the shunt current value between the all-metal integral cathode tank and the tantalum anode block is collected and converted into leakage current density data; Step S22, when the formation voltage reaches the highest target voltage value and remains in a constant voltage state, based on the real-time comparison between the leakage current density data and the preset convergence threshold, if the leakage current density data is lower than the preset convergence threshold for 10 consecutive minutes, the external DC power supply is turned off.

[0015] Preferably, the process includes an aging and correction stage, which includes the following steps: Step S6, applying the rated working voltage to the dried tantalum anode block and continuously recording the leakage current decay parameters over 100 hours; Step S7, determining the real-time leakage current change rate based on the recorded leakage current decay parameters, and when the real-time leakage current change rate is greater than 0 for 5 consecutive hours, cutting off the power supply circuit of the external DC power supply and re-immersing the tantalum anode block in the body electrolyte, and replenishing it with constant voltage at 180V for 20 minutes.

[0016] Preferably, before step S1, a vacuum heat treatment stage is included, which includes the following steps: Step S8, the tantalum anode block is fed into a vacuum sintering furnace, and the vacuum degree inside the vacuum sintering furnace is adjusted to 0.0001 Pa to 0.001 Pa; Step S9, the vacuum sintering furnace is heated to 1800°C to 1950°C at a heating rate of 15°C / min to 20°C / min, and held at this temperature range for 2 hours to 3 hours.

[0017] The present invention has at least the following beneficial effects:

[0018] 1. In improving the reliability of the dielectric layer of tantalum electrolytic capacitors, the shallow trench structure of this invention, together with the insulating inner frame, constructs a directional, vertically downward integrated formation electric field, directly cutting off the interference path of stray currents on the sidewalls. This directional electric field concentrates the electric field lines at the micropore entrance of the porous anode tantalum block, changing the local overcurrent phenomenon caused by the superposition of disordered current flow lines and micropore channel distortion in traditional processes. This spatial topological constraint forces the electric field energy to focus on the effective working surface of dielectric layer growth, eliminating the risk of ablation caused by edge discharge. The reshaping of physical boundaries adaptively ensures the stability of the electrical environment deep within the porous framework, giving the subsequent polar ion competitive migration mechanism an absolutely directional driving basis.

[0019] 2. The combination of the composite electrolyte system and the stepped voltage boosting step reconstructs the current distribution logic inside the micropores. During the voltage boosting process, transient local temperature rise occurs at the oxide film defect sites with low impedance deep within the micropores. At this time, nitrate ions with high migration rates are directly driven by the distorted electric field and preferentially migrate to the overcurrent micro-region. The accumulated polar ions form a transient polarization shielding layer in situ at the defect sites. Through its own high-resistivity intrinsic property, it temporarily reduces the local electric field of the micro-region. The overall electric field is forced to physically deflect to the surrounding non-defect regions with higher impedance by this shielding effect, thereby triggering an adaptive repair mechanism during the growth of the dielectric layer and avoiding thermal breakdown.

[0020] 3. The high-voltage step-up voltage increase and transient electric field relaxation steps are combined to overcome the ion mass transfer resistance deep in the porous framework. When the formation system is in the edge condition of continuous solute retention in high-density micropores, the continuously enhanced electric field force will cause irreversible depletion of ions participating in polarization repair deep in the micropores. The periodically applied electric field relaxation action temporarily weakens the physical driving force, causing the ions accumulated inside the pores to undergo reverse mass transfer and reach concentration equilibrium again. This dynamic adjustment process reconstructs the uniform distribution benchmark of the bulk electrolyte at the deepest part of the micropores in situ, maintains the continuity of polarization adaptive repair capability, and eliminates the physical cause of avalanche crystallization failure of the dielectric layer in the high voltage stage. Attached Figure Description

[0021] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings, in which several embodiments of the invention are illustrated by way of example and not limitation, wherein:

[0022] Figure 1 This is a process flow diagram of the method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to the present invention;

[0023] Figure 2 This is a structural diagram of the elements of the method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to the present invention.

[0024] Figure 3 This is a logic diagram of the method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to the present invention. Detailed Implementation

[0025] The principles and spirit of the present invention will now be described with reference to several exemplary embodiments in conjunction with the accompanying drawings. It should be understood that these embodiments are provided merely to enable those skilled in the art to better understand and implement the present invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the invention to those skilled in the art.

[0026] A method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor through gradient voltage boosting includes the following steps:

[0027] Step S1: Fix the tantalum anode block into the all-metal integral cathode tank with a detachable glue-free insulating inner frame, and inject the bulk electrolyte containing nitrate ions and phosphate ions. Control the bulk electrolyte to circulate in the all-metal integral cathode tank at a constant flow rate. The detachable glue-free insulating inner frame covers all the inner walls of the all-metal integral cathode tank to block the sidewall conductive channels.

[0028] Step S2, in the main formation stage, a polarization voltage is applied between the all-metal integral cathode tank and the tantalum anode block using an external DC power supply. The formation voltage provided by the external DC power supply is controlled to be progressively increased in a multi-stage progressive voltage step, including a combination of low-voltage constant current boost and high-voltage step boost, so as to deposit an amorphous tantalum pentoxide dielectric layer on the surface of the tantalum anode block.

[0029] Step S3: When the formation voltage reaches the high voltage range of 200V to 300V, an electric field relaxation operation is switched between adjacent voltage steps. Whenever the formation voltage increases by 20V, the external DC power supply is adjusted to reduce the currently applied formation voltage by 5V to 15V to generate the reduced formation voltage. The reduced formation voltage is then maintained at a constant voltage for 1min to 3min, and the multi-stage progressive voltage step is restored.

[0030] Preferably, the mass percentage concentration of nitric acid in the bulk electrolyte is 0.5% to 2.0%, and the mass percentage concentration of phosphoric acid is 10% to 15%; during the main formation stage, the temperature of the bulk electrolyte is 75°C to 85°C; before the start of the main formation stage, the liquid level of the bulk electrolyte in the all-metal integral cathode tank is 15cm to 20cm, and the circulation flow rate is 5L / min to 8L / min.

[0031] Preferably, the multi-stage progressive voltage ladder includes a low-voltage constant current boost stage and a high-voltage step boost stage; in the low-voltage constant current boost stage, the formation voltage is increased from 0V to 150V with constant current, and the constant current density is 2mA / cm² to 5mA / cm²; after the formation voltage reaches 150V, the high-voltage step boost stage is entered, and the formation voltage is increased by 5V increments per stage, and the constant voltage is maintained for 2min to 4min at each stage.

[0032] Preferably, the electric field relaxation operation in step S3 includes the following sub-steps: Step S31, whenever the formation voltage increases by 20V, the external DC power supply is controlled to reduce the currently applied formation voltage by 5V to 15V within 1s to 3s to generate the reduced formation voltage, and a bias potential difference is formed between the surface and interior of the tantalum anode block; Step S32, the ion concentration distribution of the bulk electrolyte is adjusted based on the bias potential difference, and the external DC power supply is kept in a constant voltage state for 1min to 3min under the reduced formation voltage.

[0033] Preferably, after the main formation stage is completed, the following steps are included: Step S4, the tantalum anode block is removed from the bulk electrolyte and washed in flowing deionized water at a temperature of 80°C to 90°C for 30 min to 40 min; Step S5, the washed tantalum anode block is dried in an environment at a temperature of 105°C to 115°C for 45 min to 60 min and the dried tantalum anode block is obtained.

[0034] Preferably, in step S1, the detachable glue-free insulating inner frame is made of polytetrafluoroethylene and covers the inner wall of the all-metal integral cathode tank. The vertical distance between the detachable glue-free insulating inner frame and the bottom of the all-metal integral cathode tank is 2cm to 3cm.

[0035] Preferably, the main formation stage in step S2 includes a film thickness monitoring step, which includes the following sub-steps: Step S21, in the main formation stage, the shunt current value between the all-metal integral cathode tank and the tantalum anode block is collected and converted into leakage current density data; Step S22, when the formation voltage reaches the highest target voltage value and remains in a constant voltage state, based on the real-time comparison between the leakage current density data and the preset convergence threshold, if the leakage current density data is lower than the preset convergence threshold for 10 consecutive minutes, the external DC power supply is turned off.

[0036] Preferably, the process includes an aging and correction stage, which includes the following steps: Step S6, applying the rated working voltage to the dried tantalum anode block and continuously recording the leakage current decay parameters over 100 hours; Step S7, determining the real-time leakage current change rate based on the recorded leakage current decay parameters, and when the real-time leakage current change rate is greater than 0 for 5 consecutive hours, cutting off the power supply circuit of the external DC power supply and re-immersing the tantalum anode block in the body electrolyte, and replenishing it with constant voltage at 180V for 20 minutes.

[0037] Preferably, before step S1, a vacuum heat treatment stage is included, which includes the following steps: Step S8, the tantalum anode block is fed into a vacuum sintering furnace, and the vacuum degree inside the vacuum sintering furnace is adjusted to 0.0001 Pa to 0.001 Pa; Step S9, the vacuum sintering furnace is heated to 1800°C to 1950°C at a heating rate of 15°C / min to 20°C / min, and held at this temperature range for 2 hours to 3 hours.

[0038] Example 1: In an industrial chemical synthesis system using a 316L stainless steel integral tank as the cathode, the tank sidewall is lined with a polytetrafluoroethylene glue-free insulating inner frame, forming a single vertical conductive surface at the bottom of the tank. The tank depth is set to 20mm. A porous anode tantalum block is placed in the center of the cathode tank, and an electrolyte with a phosphoric acid concentration of 0.6mol / L and a nitric acid addition of 150ppm is injected. The electrolyte flow rate is controlled to maintain a constant concentration field within the tank, and the electrolyte temperature is maintained at 65℃.

[0039] During the main formation stage, a formation voltage is applied by a DC power supply. When the formation voltage rises to a high-voltage range above 200V, the formation process operates in a segmented gradient voltage increase manner. Whenever the formation voltage increases by 20V, the system triggers an electric field relaxation operation: the formation voltage is reduced by 10V and held at this voltage for 2 minutes, then the original gradient path is restored. This process reduces the local electric field strength, driving phosphate and nitrate ions in the electrolyte to transfer mass deep into the micropores of the porous anode tantalum block. At the micropore defect sites, the preferential polarization migration of nitrate ions is utilized to construct a transient polarization shielding layer. This polarization shielding layer forces the vertically downward distributed formation electric field lines to deflect towards non-defect sites, thus reducing the amorphous state in the defect-free region. As the oxide film thickens at a uniform rate, the local electric field distortion is eliminated when the polarization impedance at the defect site becomes consistent with the impedance of the surrounding intrinsic film layer. The polarization shielding layer then dissociates. After multiple stages of stepped voltage boosting and electric field relaxation cycles, a dense and continuous dielectric layer is formed on the surface of the porous anode tantalum block. Compared with the traditional linear voltage boosting process, the leakage current of the tantalum anode block obtained by using this gradient formation scheme is reduced by 45%, and the breakdown voltage is increased by 18%. In long-term electrothermal stress testing, it exhibits insulation stability that is highly correlated with the amorphous oxide film structure.

[0040] Example 2: The current experiment was conducted in the same cathode tank and porous anode tantalum block environment as in the previous example. To objectively quantify the effect of electric field relaxation operation on the polarization shielding mechanism of dielectric layer defect sites, a control test group with different voltage reduction amplitudes and holding times was designed to observe the evolution trend of leakage current and breakdown voltage. The test group adopted a gradient voltage reduction path: during the process of increasing the formation voltage from 200V to 300V, whenever the formation voltage increased by 20V, a voltage reduction of 10V was applied and held constant for 2 minutes, and then the original gradient voltage increase was restored. The low-intensity control group adopted a mild relaxation path: for every 20V increase, the voltage was reduced by 4V and held constant for 1 minute. The high-intensity control group adopted a reinforced relaxation path: for every 20V increase, the voltage was reduced by 16V and held constant for 4 minutes. All the above test groups terminated the experiment when the formation voltage reached 300V, and the breakdown voltage of the obtained tantalum anode block was uniformly tested using a withstand voltage tester.

[0041] Experimental data records show that the leakage current of the dielectric layer obtained in the sample group of this invention is stable at 2.5 μA / cm², and the breakdown voltage is concentrated at 330V. In the low-intensity control group, due to the lower reduction amplitude, the electrolyte concentration gradient deep within the micropores cannot be effectively restored, resulting in limited formation efficiency of the polarization shielding layer at defect sites. Ultimately, the leakage current rises to 8.2 μA / cm², and the breakdown voltage exhibits significant dispersion, ranging from 280V to 310V. In the high-intensity control group, due to the prolonged relaxation time and the influence of a continuous low voltage state, the overall growth rate of the dielectric layer is slower, resulting in a total film thickness reduction of approximately 15% compared to the sample group of this invention. Thermal degradation occurs under 320V conditions. The analysis of the physical mechanism leading to breakdown shows that there is an optimal engineering window for the voltage reduction amplitude and holding time. Under the conditions of 10V reduction amplitude and 2min holding time, the formation electric field and ion mass transfer process achieve transient dynamic equilibrium, and the polarization shielding effect of the defect site is the most significant. When the reduction amplitude is lower than the lower limit, the solute concentration in the depth of the micropore is insufficient to support the stable construction of the polarization shielding layer. When the reduction amplitude is higher than the upper limit, the intrinsic growth rate of the dielectric layer is significantly delayed due to the continuous interception of the formation electric field, sacrificing the compactness of the film. The experimental data confirms that this parameter combination maximizes the repair efficiency of the defect site while ensuring the uniformity of the dielectric layer thickness.

[0042] Example 3: This example combines Figures 1 to 3 This paper describes a method for improving the reliability of the dielectric layer in tantalum electrolytic capacitors using a gradient voltage boosting technique. Figure 1 As shown, the process involves fixing the tantalum anode block and controlling the circulation of the electrolyte in the bulk solution. It then proceeds to a process of controlling the formation voltage to increase in a multi-stage progressive voltage gradient. During operation, the process continuously checks whether the formation voltage has reached the high-voltage range. If the result indicates that the high-voltage range has not been reached, the process returns to continue controlling the formation voltage to increase in a multi-stage progressive voltage gradient. If the result indicates that the high-voltage range has been reached, the formation voltage is reduced and an electric field relaxation operation is initiated. The reduced formation voltage is then maintained at a constant voltage. Finally, the multi-stage progressive voltage gradient is restored, and the process cycles back to the control of the formation voltage to increase in a multi-stage progressive voltage gradient.

[0043] like Figure 2 As shown, to achieve the core objective of improving the reliability of the dielectric layer of tantalum electrolytic capacitors, the technical solution of this invention mainly includes four parts. In the dimension of tank structure optimization, it includes an all-metal integral cathode tank and a detachable glue-free insulating inner frame to block the conductive channels on the side walls. In the dimension of composite electrolyte system, it includes nitrate and phosphate ions circulating at a constant flow rate to prevent the depletion of polar ion mass transfer. In the dimension of gradient voltage boosting mechanism, it includes a low-voltage constant current boosting stage and a high-voltage step boosting stage to suppress local overcurrent and Joule heating. In the dimension of electric field relaxation operation, it includes cutting into the electric field relaxation operation and periodically adjusting the degradation voltage to achieve the process state of reconstructing the concentration balance deep in the channel.

[0044] like Figure 3 As shown, there is a close interaction between various process elements and structural units. The detachable glue-free insulating inner frame points to the low-voltage constant current boost stage, which acts on the all-metal integral cathode tank, the electric field relaxation operation, and the amorphous tantalum pentoxide dielectric layer to improve the reliability of the dielectric layer. The all-metal integral cathode tank further points to the high-voltage stepped boost stage, which simultaneously points downward to the body electrolyte, to the right to the transient polarization shielding layer, and upward to the amorphous tantalum pentoxide dielectric layer in the core area to improve the reliability of the dielectric layer. At the same time, the electric field relaxation operation points downward to the bias potential difference, which then points downward to the transient polarization shielding layer. The body electrolyte also points to the transient polarization shielding layer to the upper right. Finally, the transient polarization shielding layer points to the amorphous tantalum pentoxide dielectric layer in the core area to the left to improve the reliability of the dielectric layer.

[0045] Example 4: In the mass production of tantalum electrolytic capacitors, multiple anode tantalum blocks are installed in parallel within an all-metal integral cathode tank. A constant flow rate of electrolyte circulation ensures that each anode tantalum block is in a uniform physical field environment. To reduce the risk of localized over-formation caused by porosity differences during mass production, a current density monitoring feedback loop is deployed in the production system. This loop performs real-time closed-loop control based on the rate of change of the total current density in the tank, and the system continuously monitors the total current density of the tank. And calculate the rate of change per unit time. When the formation voltage is in the range of 200V to 300V, if the rate of change is lower than the preset critical value... The system determines that solute depletion occurs deep within the micropores; this critical value... Based on historical formation data fitting, it is defined as the ratio of the decrease in current density per unit time to the total current density, reflecting the slowdown in oxide film growth rate.

[0046] At this point, the system performs an electric field relaxation operation, adjusting the current formation voltage to the target voltage set by the formation power supply. 85%, and maintain that voltage until Restore to To compensate for the differences in electric field distribution caused by the different positions of the anode tantalum blocks in cluster production, a voltage compensation operator is introduced into the system. The compensation operator corrects the applied voltage in real time using the following formula: ,in, The effective formation voltage applied to the tantalum anode block, The target voltage set for the formation power supply. This is the voltage compensation amount, which is given by the formula... The decision, among which, The compensation coefficient represents the sensitivity of voltage bias to current density. This represents the total current density of the tank currently being monitored. The reference current density is used under standard operating conditions. When the total current density of the monitoring tank is higher than the standard reference value, the system reduces the effective voltage and forces the electric field to deflect towards the unreacted region with higher impedance.

[0047] The offline calibration process is used to determine the engineering window for relaxation parameters: before production operation, the impedance frequency spectrum is measured at different electrolyte concentrations. By determining the range in which the capacitance value changes most smoothly with frequency, the holding time under standard operating conditions is locked at 2.2 min. The above control logic and calibration process ensure that the thickness deviation of the tantalum pentoxide dielectric layer is within 3% in batch production, and that each anode tantalum block exhibits high engineering consistency in the breakdown voltage test.

[0048] Example 5: In the formation workshop of industrial-grade high-voltage tantalum electrolytic capacitors, multiple tantalum anode blocks are arrayed and installed in an all-metal integral cathode tank. The electrolyte is maintained in circulation at a constant flow rate to ensure the mass transfer consistency of the porous skeleton surface. In order to deal with the differences in electrical performance of tantalum anode blocks of different specifications during the formation process, the system deploys a baseline calibration and parameter fine-tuning procedure based on electrochemical impedance spectral data in the main formation stage to solve the risk of high-voltage breakdown caused by fixed formation parameters.

[0049] Before deploying this formation process, the system performs offline calibration on the current batch of tantalum anode blocks. Five representative tantalum anode blocks from this batch are selected as samples. At a rated voltage of 200V, impedance spectrum data in the frequency range of 0.1Hz to 100kHz are obtained using an electrochemical impedance spectroscopy (EIS) meter. By fitting the impedance spectrum, the characteristic frequency point corresponding to the intrinsic impedance of the tantalum pentoxide oxide film is determined. When the impedance value corresponding to this characteristic frequency point is lower than a preset safety threshold... At that time, the system determined that the initial defect density of this batch of tantalum anode blocks was high, among which, The numerical values ​​are determined based on the statistical range of hundreds of batch tests in the previous stage, and are used to quantitatively distinguish between qualified products and products with a high defect tendency. Based on this offline calibration data, the system automatically calculates and updates the gradient boost slope of the formation power supply. ,in ,in, For standard boost slope, This represents the impedance value measured at the characteristic frequency of the current batch. This is the impedance reference value corresponding to the historical standard batch.

[0050] In the actual formation process, the system utilizes this calibrated and corrected boost slope. The driving voltage is increased to maintain a physical match between the growth rate of the dielectric layer and the oxidation capacity of the porous structure. When transient surface temperature rise fluctuations are detected inside the anode tantalum block, the system invokes the correction operator. The formation voltage is adjusted in microsecond-level response, wherein... This is the voltage bias calibration value. The temperature-sensitive response coefficient, This represents the current real-time monitored transient temperature of the anode surface. Using the ambient reference temperature, this voltage bias calibration adjusts the formation power supply output in real time to counteract localized overheating of the surface layer caused by abnormal local current density at defect sites, ensuring that the tantalum pentoxide dielectric layer remains in a uniform growth kinetic environment within the porous framework. To detect and adjust surface temperature rise fluctuations, the control system indirectly senses localized heat conduction deep within the micropores of the porous framework through electrical signal conversion. Specifically, when a transient surface temperature rise occurs at a defect site in the porous framework, the micro-region experiences a sudden surge in localized leakage current due to thermally induced charge carriers. This abrupt change in the surface electrical signal is superimposed on the overall total current of the entire formation circuit in real time. The system uses a high-frequency current transformer installed in the formation power supply circuit to capture the high-frequency perturbation signal of this overall total current in real time at a sampling frequency of 50 MHz, and uses a differential operation model to demodulate the equivalent electrical temperature rise amplitude corresponding to the surface defect location. The calculation formula is as follows: ,in, This is the equivalent electrical temperature rise value. For conversion factors, The captured high-frequency perturbation signal current value; and then based on the formula This data is converted into the transient temperature of the anode surface that the control system can recognize in real time. When the demodulated electrical temperature data shows a sudden signal that exceeds the reference fluctuation, the power control module directly cuts off or de-polarizes the voltage through the hardware-level field-effect transistor drive circuit. This blocks the continuous accumulation of Joule heat at the defect site within microseconds, avoiding the time delay of heat conduction in physical conduction. This achieves complete self-consistency in logic and physics for cross-scale control. Through the combination of offline baseline calibration and microsecond-level bias calibration during operation, the batch-to-batch leakage current stability index is improved by 15%, effectively ensuring the electrical structural integrity of the dielectric layer.

[0051] Example 6: In the mass formation process of industrial-grade tantalum electrolytic capacitors, a set of tantalum anode blocks to be treated are loaded into an all-metal cathode tank lined with polytetrafluoroethylene. The sidewall lining structure of the tank is used to block the sidewall conductivity, forming a vertical conductive interface at the bottom. A phosphoric acid electrolyte with a concentration of 0.6 mol / L is injected into the tank, which contains 150 ppm of nitrate ions. A constant flow rate of electrolyte is maintained during the formation process.

[0052] When the DC power supply boosts the formation voltage to a high-voltage range of over 200V, the formation system enters the gradient boost mode. The system executes the following parameter calibration procedure: with a voltage boost step of 20V, after each step, the system sends a voltage reduction command to the electric field execution unit to reduce the instantaneous formation voltage by 10V and maintain it at this reduced voltage for 2.2 minutes. This reduction operation aims to induce a transient polarization shielding effect. When nitrate ions in the electrolyte are driven by the electric field force into the porous microporous structure of the tantalum anode block, they work together with phosphate ions at the microporous defect sites to construct a polarization shielding layer, forcing the formation electric field lines to deflect towards the surrounding non-defective regions with higher impedance, causing the tantalum pentoxide dielectric layer in the non-defective regions to thicken uniformly.

[0053] The system monitors the total current density of the formation tank. The unit is And using the rate of change of current density Characterizing the mass transfer state deep within micropores, From the formula It is confirmed that, among them, The change in current density The sampling time interval is when the detected The value is lower than the preset threshold. When the system determined that solute mass transfer was limited deep within the micropores, offline impedance frequency spectrum analysis confirmed that a holding time of 2.2 minutes was sufficient to complete the concentration relaxation process deep within the micropores under the given concentration and temperature conditions. After the formation process, leakage current and breakdown voltage tests were performed on the resulting tantalum anode blocks. Under the aforementioned gradient voltage boost and electric field relaxation operation, the measured leakage current of the tantalum anode blocks was 2.5 μA / cm², and the breakdown voltage reached 330 V. If the electric field relaxation operation was removed, the measured leakage current of the same batch of tantalum anode blocks increased to 8.2 μA / cm², and the breakdown voltage was distributed in the range of 280 V to 310 V. The data results indicate that by combining voltage reduction with constant voltage holding, a dynamic balance between electric field distribution and solute mass transfer was achieved, enhancing the structural uniformity of the tantalum pentoxide dielectric layer.

[0054] The above description is only a few preferred embodiments of the present invention and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present invention is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the above-mentioned inventive concept. For example, technical solutions formed by replacing the above-mentioned features with the technical features with similar functions disclosed in the embodiments of the present invention.

Claims

1. A method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor by gradient voltage boosting, characterized in that, Includes the following steps: Step S1: Fix the tantalum anode block into the all-metal integral cathode tank with a detachable glue-free insulating inner frame, and inject the bulk electrolyte containing nitrate ions and phosphate ions. Control the bulk electrolyte to circulate in the all-metal integral cathode tank at a constant flow rate. The detachable glue-free insulating inner frame covers all the inner walls of the all-metal integral cathode tank to block the sidewall conductive channels. Step S2, in the main formation stage, a polarization voltage is applied between the all-metal integral cathode tank and the tantalum anode block using an external DC power supply. The formation voltage provided by the external DC power supply is controlled to be progressively increased in a multi-stage progressive voltage step, including a combination of low-voltage constant current boost and high-voltage step boost, so as to deposit an amorphous tantalum pentoxide dielectric layer on the surface of the tantalum anode block. Step S3: When the formation voltage reaches the high voltage range of 200V to 300V, an electric field relaxation operation is switched between adjacent voltage steps. Whenever the formation voltage increases by 20V, the external DC power supply is adjusted to reduce the currently applied formation voltage by 5V to 15V to generate the reduced formation voltage. The reduced formation voltage is then maintained at a constant voltage for 1min to 3min, and the multi-stage progressive voltage step is restored.

2. The method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to claim 1, characterized in that, The mass percentage concentration of nitric acid in the bulk electrolyte is 0.5% to 2.0%, and the mass percentage concentration of phosphoric acid is 10% to 15%. During the main formation stage, the temperature of the bulk electrolyte is 75°C to 85°C. Before the start of the main formation stage, the liquid level of the bulk electrolyte in the all-metal integral cathode tank is 15cm to 20cm, and the circulation flow rate is 5L / min to 8L / min.

3. The method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to claim 1, characterized in that, The multi-stage progressive voltage ladder includes a low-voltage constant current boost stage and a high-voltage step boost stage. In the low-voltage constant current boost stage, the formation voltage is increased from 0V to 150V with a constant current density of 2mA / cm² to 5mA / cm². After the formation voltage reaches 150V, the high-voltage step boost stage is entered, and the formation voltage is increased by 5V increments per stage, and the voltage is kept constant for 2 to 4 minutes at each stage.

4. The method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to claim 1, characterized in that, The electric field relaxation operation in step S3 includes the following sub-steps: Step S31, whenever the formation voltage increases by 20V, the applied DC power supply is controlled to reduce the currently applied formation voltage by 5V to 15V within 1s to 3s to generate the reduced formation voltage, and a bias potential difference is formed between the surface and interior of the tantalum anode block; Step S32, the ion concentration distribution of the bulk electrolyte is adjusted based on the bias potential difference, and the applied DC power supply is kept in a constant voltage state for 1min to 3min under the reduced formation voltage.

5. The method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to claim 1, characterized in that, After the main formation stage is completed, the following steps are included: Step S4, the tantalum anode block is removed from the bulk electrolyte and washed in flowing deionized water at a temperature of 80°C to 90°C for 30 min to 40 min; Step S5: the washed tantalum anode block is dried in an environment at a temperature of 105°C to 115°C for 45 min to 60 min and the dried tantalum anode block is obtained.

6. The method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to claim 1, characterized in that, In step S1, the detachable glue-free insulating inner frame is made of polytetrafluoroethylene and covers the inner wall of the all-metal integral cathode tank. The vertical distance between the detachable glue-free insulating inner frame and the bottom of the all-metal integral cathode tank is 2cm to 3cm.

7. The method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to claim 1, characterized in that, Step S2, the main formation stage, includes a film thickness monitoring step, which includes the following sub-steps: Step S21, in the main formation stage, the shunt current value between the all-metal integral cathode tank and the tantalum anode block is collected and converted into leakage current density data; Step S22, when the formation voltage reaches the highest target voltage value and remains in a constant voltage state, based on the real-time comparison between the leakage current density data and the preset convergence threshold, if the leakage current density data is lower than the preset convergence threshold for 10 consecutive minutes, the external DC power supply is turned off.

8. The method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to claim 5, characterized in that, The process includes an aging and correction stage, which includes the following steps: Step S6, applying the rated working voltage to the dried tantalum anode block and continuously recording the leakage current decay parameters over 100 hours; Step S7, determining the real-time leakage current change rate based on the recorded leakage current decay parameters, and when the real-time leakage current change rate is greater than 0 for 5 consecutive hours, cutting off the power supply circuit of the external DC power supply and re-immersing the tantalum anode block in the body electrolyte, and replenishing it with constant voltage at 180V for 20 minutes.

9. The method for improving the reliability of the dielectric layer of a tantalum electrolytic capacitor using gradient voltage boosting according to claim 1, characterized in that, Before step S1, a vacuum heat treatment stage is included, which includes the following steps: Step S8, the tantalum anode block is fed into a vacuum sintering furnace, and the vacuum degree inside the vacuum sintering furnace is adjusted to 0.0001 Pa to 0.001 Pa; Step S9, the vacuum sintering furnace is heated to 1800°C to 1950°C at a heating rate of 15°C / min to 20°C / min, and held at the temperature for 2 hours to 3 hours.

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