Electrolytic Capacitors Research Articles

Carbon Nanostructures Derived from In Situ Grown ZIF Nanocages within Bacterial Cellulose for AC-Filtering Electrochemical Capacitors.

Electrochemical capacitors (ECs) offer superior specific capacitance for energy storage compared to traditional electrolytic capacitors but face limitations in alternating current (AC) filtering due to the need for balancing fast response and high capacitance. This study addresses these challenges by developing a freestanding nanostructured carbon electrode, derived from the rapid carbonization of bacterial cellulose (BC) embedded with zeolitic imidazolate framework 8 (ZIF-8) and in situ formed carbon nanotubes (CNTs). The electrode exhibits an exceptionally low area resistance of 9.8 mΩ cm2 and a high specific capacitance of 2.1 mF cm-2 at 120Hz, maintaining performance even at high frequencies. Stacking these electrodes enhances the capacitance to 5.3 mF cm-2, with the phase angle degrading to -74.4° at 120Hz; however, they retain a phase angle below -45° up to ≈50kHz, demonstrating excellent high-frequency performance. Furthermore, connecting three aqueous units in series as an integrated cell or utilizing organic electrolytes extends the voltage window to 2.4V, enhancing their suitability for high-voltage applications. Ripple voltage analysis under various loads and frequencies indicates effective filtering capabilities, highlighting the potential of these nanostructured ECs for next-generation electronic applications.

Novel Single-Stage Electrolytic Capacitor-Less Buck-Boost Inverter

Nowadays, single-phase, single-stage, buck-boost power inverters are mostly considered to be used for renewable energy source applications due to their wide range of capabilities. This article introduces a novel, single-phase, single-stage, buck-boost inverter with a wide range of input DC voltage. In addition, the introduced inverter does not use the electrolytic capacitor, which enhances the lifetime and volume reduction in the inverter, avoids the high equivalent series resistance, and reduces the inrush current of electrolytic capacitors in the introduced inverter. Moreover, the introduced inverter exhibits a reduced switch voltage rating, and the novel PWM control strategy with the half-cycle of the sinusoidal is derived to reduce the switching loss of power switches, thus improving the inverter’s efficiency. The operation states, theoretical analysis, and design of components are fully discussed. A comparative study of the introduced inverter with other buck-boost inverter topologies is also reported. Finally, the 500 W laboratory prototype is set up for simulation and experimental verification. The experimental results verify the correctness of operating analysis and simulation.

Highly Durable Sn-Ni Alloy Anode Pretreated in Vinylene Carbonate-Containing Electrolyte for Lithium-Ion Capacitors

Abstract Lithium-ion capacitors (LICs) are promising energy storage devices for electric vehicles because they rank between LIBs and EDLCs in terms of energy and power density. In a previous work, an LIC with a Sn-Ni alloy anode was proven to be superior in terms of energy and power density compared to that with a graphite anode. To improve the cycle durability at a practical level, the effect of vinylene carbonate (VC), which positively affects LIBs, was investigated. VC demonstrates a positive effect during the pre-treatment process, but also a negative effect during charge-discharge cycling. The difference between these effects is discussed in terms of the potential and morphology changes of the anode, revealing that the VC forms a polymer-like solid electrolyte interphase during the pre-treatment process, suppressing the deactivation of Sn caused by crack growth and peeling off during charge-discharge cycling. In contrast, VC continuously decomposes during charge-discharge cycling while consuming pre-treated lithium. Finally, an excellent cycle durability (10,000 cycles with a capacity retention of 72.3%) is here demonstrated for the first time for the LIC with a high volumetric energy density of 38.9 Wh/L at 120 W/L.

Discharge-Based Condition Monitoring for Electrolytic DC-Link Capacitors

Discharge-Based Condition Monitoring for Electrolytic DC-Link Capacitors

An Online Monitoring Method for DC Busbar Electrolytic Capacitor Bank Based on Optimized Rogowski Coil Current Sampling

An Online Monitoring Method for DC Busbar Electrolytic Capacitor Bank Based on Optimized Rogowski Coil Current Sampling

Analysis of the influence of power supply on control and protection device for voltage source converter-based high voltage direct current

Abstract The high-frequency DC switching power supply is a core module in control and protection devices for voltage source converter-based high voltage direct current (VSC-HVDC) systems. In practice, this type of power supply is often prone to failure. This paper investigates the working circuit of the switching power supply and examines various quality issues with power supply components. It focuses on aluminum electrolytic capacitors and key circuit DC/DC converters, which are particularly failure-prone. The study establishes a model for these components and analyzes the effects of capacitance reduction and increased equivalent series resistance, which result from capacitor failures. Through simulation experiments, the research explores the impact of these quality issues on DC/DC circuits. This work lays the foundation for understanding how the power module affects the VSC-HVDC protection device.

Glyoxal-based electrolytes in potassium-ion capacitors

Potassium-based energy storage systems demonstrate promising potential for use in high-power applications, such as potassium-ion capacitors (PICs). In this study, we present the use of an electrolyte containing 1,1,2,2-tetraethoxyethane (TEG) in combination with propylene carbonate (PC) and potassium bis(fluorosulfonyl)imide (KFSI) as electrolyte for PICs. We have shown that using this electrolyte and applying a designed test protocol, it is possible to realize PICs with good capacity and cycling stability. The high performance is possible due to the high-rate capability of the graphite electrodes in the proposed electrolyte. Subsequent analysis of the electrodes reveals both structural changes of the graphite electrode and changes in the chemical composition of the AC and graphite electrode surfaces.

Electric Double-Layer Capacitance on Carbon Electrodes in Concentrated Aqueous Electrolytes of Alkaline Metal Salts

Introduction: Electric double layer capacitors (EDLCs), which store electricity by adsorption and desorption of ions, are commercialized for mobile devices and vehicles due to their high-rate capability and long cycle life. However, the lower energy densities of EDLCs than batteries limit their applications. Thus, much attention has been paid to improving their energy densities (E), described by the equation E = 1/2 CV2, where C is the capacitance, and V is the operating cell voltage1). Here, we focused on aqueous electrolytes, which are superior to organic electrolytes used in most commercial EDLCs, in terms of safety, cost, ionic conductivity, and permittivity2). However, the narrow potential window by theoretical water splitting voltage limits the operating voltage of aqueous EDLCs. Recently, highly concentrated aqueous electrolytes, referred to as hydrate-melts3), have been developed, enabling high-voltage operation of aqueous energy-storage devices, including aqueous EDLCs. In this context, it is desired to investigate the influences of electrolyte compositions on double layer capacitances in concentrated aqueous electrolytes. In most previous studies, the performance evaluation, including capacitance in each electrolyte, was performed with activated carbon electrodes used for commercial EDLCs, demonstrating the feasibility of relatively concentrated aqueous electrolytes for EDLCs4). However, the capacitance of activated carbon electrodes may be affected by various non-intrinsic factors including viscosity. Therefore, capacitance evaluation, eliminating various effects of non-EDL related factors, is required to gain a fundamental understanding of the electric double layer in highly concentrated aqueous electrolytes as well as establish an electrolyte design strategy to improve energy density.In this study, we studied the EDL capacitance in concentrated aqueous electrolytes. To exclude the influence of electrolyte viscosity, we used a flat carbon plate as a model electrode and evaluated the EDL capacitance by electrochemical impedance spectroscopy (EIS). The EDL capacitance was evaluated in aqueous electrolytes with various concentrations of alkali-metal salts to gain basic insights into the design of aqueous electrolytes for EDLCs. Experimental: EIS was performed in the frequency range of 100 kHz–1 Hz at 30°C with three-electrode cells (with glassy carbon, Pt mesh, and Ag/AgCl as a working, counter, and reference electrodes, respectively) to evaluate the capacitances in 100 Hz at various potentials in aqueous electrolytes. KN(SO2F)2 (KFSI) with concentrations ranging from 1.1 mol kg-1 (m) to 30.8 m, 61.7 m K(N(SO2F)2)0.55(SO3CF3)0.45 (K(FSI)0.55(OTf)0.45), 21 m NaFSI, 21 m LiN(CF3SO2)2 (LiTFSI) were used as electrolytes. Results & Discussion: The EIS results show that the capacitance of glassy carbon in KFSI/H2O reached its maximum at 22.2 m (Fig.1a). Further increasing the salt concentration up to 61.7 m K(FSI)0.55(OTf)0.45/H2O monotonically decreased the capacitance. This trend is different from those reported for activated carbon electrodes, at which the capacitance monotonically increased with increasing concentration5). This difference may result from the electrolyte viscosity, which can differently affect the flat glassy carbon and porous activated carbon. We also studied various alkaline-metal salt electrolytes at the same 21 m concentrations (Fig.1b). The capacitance at glassy carbon electrodes increased in the order of LiTFSI<NaFSI<KFSI, suggesting that larger cations result in higher capacitances. In the presentation, we will discuss how the electrolyte components and concentrations dominate EDL structures and capacitances on carbon electrodes in aqueous electrolytes. Acknowledgement: This study was partially supported by JSPS KAKENHI Grant Number JP 24H00483 and Mitsubishi Foundation.

(Invited) In Situ Crosslinked Gel Polymer Electrolytes for Li-Ion Capacitors with Improved Safety and Stability at High Temperature Operation

Li-ion capacitors (LICs) are considered a promising option for high-power application with a relatively high energy content compared to traditional supercapacitors1. There are however some issues with LICs: The anode needs to be pre-lithiated, which adds extra processing steps and increases the cost of assembly and/or material, and the stability at elevated temperatures and flammability of organic electrolytes often used in LICs. Recent progress regarding the pre-lithiation has been made by researchers at CIC energiGUNE, by using as a sacrificial salt together with hard carbon as anode2. Regarding novel electrolytes, polymer electrolytes (PEs) are considered a promising route to improve stability and increase the safety in battery research. However, the low ionic conductivity at room temperature limits high-power performance. Overall, important properties of electrolytes for LICs are a wide electrochemical stability window, high conductivity, and a low viscosity. For a PE to fulfil these demands, a liquid component is added to the polymer, forming a gel polymer electrolyte (GPE). In this work, we have investigated a mixture of two monomers, PETEA and PEGDMA, as polymer components in a standard 1M LiFSI EC:DMC liquid electrolyte. This polymer mixture enables the formation of a GPE in situ, at very low concentrations, through a mild heat treatment. Results have been shown in slightly different systems to provide a high conductivity and wide electrochemical stability windows3. In this work we show that the GPE is compatible with the sacrificial salt and that the addition of a polymer component reduces evaporation and improves stability and performance at 70 and 80ºC compared to the liquid electrolyte alone.

(Invited) Plasma-Tailored Nanocarbons As Advanced Electrodes for High-Frequency Supercapacitors

Increasing demand for miniatured electronic devices with high power efficiencies and energy densities led to the exponential growth of electrochemical capacitors. Currently, the available electrochemical capacitors deliver the highest performance at direct current (DC), mainly in the low-frequency regions (less than 1 Hz) due to their electrode architecture and configurations. Therefore, using electrochemical supercapacitors in commercial applications is still in the initial phase. The use of such systems in large-scale electricity applications is also limited due to the insufficient response in the alternating current (AC). Considering that energy storage devices mostly deliver high performance at DC, it is crucial to design a device that responds to AC power sources which can sufficiently convert AC to DC for consumer needs. Therefore, the research interest in line-filtering supercapacitors is gaining attention nowadays. Such supercapacitors have been highly influenced by the design and architecture of the electrode material employed. Electrical conductivity of the electrode material, minimum contact resistance between the active material and current collector, thickness between 1-10 μm and microstructure design are critical for designing high-performing line filtering supercapacitors. Directly depositing the active material on the current collector without using polymeric binders is crucial for designing electrodes with such features. Among different deposition techniques, plasma-enhanced chemical vapour deposition stands out due to its advantages for designing nanostructures directly on substrates with different morphology, orientation, dimensions and thicknesses. This paper presents the advantage of plasma for the structure-controlled designing and tailoring of carbon nanostructures as advanced electrodes in supercapacitors for AC to DC line filtering applications. The plasma-deposited vertical carbon nanostructure electrodes achieved a capacitance of 430 μF in the high-frequency range (100 Hz) and displayed a phase angle of ∼ -80°. Besides, a prismatic prototype was designed to investigate the stability and filtering efficiency of the electrodes to convert AC to DC, which displayed a capacitance of 12 mF at 100 Hz with long-term filtering stability (above 3 h). The excellent filtering efficiency of supercapacitors made of plasma-designed carbon nanostructures opened up new paradigms to replace conventional aluminium electrolytic capacitors for high-frequency performances.

Evaluation of the Dielectric Properties of Aluminum Conductive Polymer Solid Capacitors at High Temperatures

Aluminum capacitors have a unique combination of properties that highlight them as potential devices for power electronic applications, such as high capacitance, low cost, and high energy density. When combined with a polymeric conductive media, such as PEDOT:PSS, it outperforms traditional electrolytic capacitors in terms of thermal stability, showing a high ripple current with a low equivalent series resistance (ESR). The low breakdown voltage of commercially available devices (~100 V) has limited their applications in many fields of electronics. Nonetheless, current scientific research has found that crystalline coatings, with subsequent immersion in hot water (95 °C), are a good alternative to enhance the breakdown potential (≥ 600 V) of conductive polymer solid capacitors, especially when operated at room temperature; in addition, the leakage current can be effectively controlled through a re-anodizing procedure [1,2]. The current market needs capacitors that can reach high withstand potentials (≥ 600 V) in an operation range of up to 200 °C, and reports on solid polymer capacitor performance at high potentials and temperatures are scarce. Here, the performance at high temperatures (≤ 200 °C) of crystalline anodic coatings with subsequent hot water immersion was assessed, and the results were compared with a post-hydrated sample with a re-anodizing process at 400 V. Finally, a possible degradation mechanism at high temperatures was explored.The dielectric material was formed as follows. First, an electropolished high-purity aluminum sheet was immersed in hot water (95 °C) for 10 min to form a pseudo-boehmite layer. The anodization was conducted at 700 V in H3BO3 solution at 85 °C for 10 min, followed by immersion in hot water at 95 °C for 10 min. To control the dielectric defects, a re-anodizing process at 400 V was performed at 85 °C for 10 min in H3BO3 solution. The PEDOT:PSS conductive polymer was coated on the dielectric material using an aqueous dispersion solution of ~1% concentration. The dielectric properties were assessed by AC impedance spectroscopy and voltage sweeping in a model flat aluminum capacitor with a PEDOT:PSS conductive polymer as the cathode at high temperatures (≤ 200 °C).The thermal stability analysis evidenced that the aluminum capacitor with a subsequent immersion in hot water assessed with a PEDOT:PSS conductive polymer remained dielectrically invariable up to 100 ˚C, with a breakdown potential of ~790 V. Nonetheless, the breakdown potential was reduced when the temperature was increased to 200 °C with an average value of ~473 V. Analogous behavior was observed in the aluminum capacitor with re-anodization at 400 V, where the breakdown potential remained constant with a value of ~ 670 V up to 100 °C; however, an increase in the temperature to 200 °C reduced its value until ~550 V. Hence, thermal analysis revealed that the post-anodizing treatments aimed at enhancing the breakdown potential (˃600 V) of crystalline coatings at ambient temperature [2] fail to sustain the withstand voltage above 600 V as the temperature increases to a maximum value of 200°C. Furthermore, an in-parallel examination in which the dielectric layer without the PEDOT:PSS coating was heated to 200 °C showed that thermal degradation mostly affects the dielectric layer.Surface and cross-sectional analyses by SEM showed that a crucial aspect of the breakdown potential enhancement is on the PEDOT:PPS-dielectric layer interface. The formation of a nanovoid layer by immersion in hot water avoids the local current concentration at high voltages and modifies the electrical resistance in the PEDOT:PSS-dielectric material interface. SEM cross-sectional observations of the dielectric layer at high temperatures (≤ 200 °C) show that the nanovoid layer remains visible; nevertheless, a porosity analysis by pore-filling reveals that the porosity in the nanovoid layer increases with temperature, modifying the PEDOT:PSS-dielectric layer interaction. Although the reason for the low breakdown potential in solid polymer capacitors is still unclear, from the light of the present results, the PEDOT: PSS-dielectric layer interaction is shown to be an important factor.This work was supported by the MEXT-Program for Creation of Innovative Core Technology for Power Electronics Grant Number JPJ009777.

(Invited) Improving Withstand Voltages of Conductive Polymer Solid Aluminum Capacitors for Power Electronics Applications

Aluminum solid electrolytic capacitors using conductive polymer cathodes are promising passive components with high capacitance, low equivalent series resistance (ESR) and high thermal stability for applications in advanced power electronics systems. However, the working voltage of the aluminum solid capacitors is limited and does not meet the requirements of the power electronic systems. In this study, two approaches are introduced to increase the withstand voltage of the aluminum solid capacitors: introducing a highly resistive interface layer between a dielectric alumina layer and a conductive polymer layer and the development of novel modified PEDOT:PSS polymers.When a crystalline g’-alumina dielectric layer covered with a porous hydrated alumina layer was coated with a PEDOT:PSS conductive polymer, the breakdown voltage was ~500 V for the dielectric alumina film formed at 700 V. The dielectric breakdown occurred at voltages considerably lower than the anodizing voltage. However, the introduction of the simple hot water treatment after anodizing (post-hydration treatment) increased the breakdown voltage markedly, exceeding the anodizing voltage of 700 V.1 Cross-sectional STEM observation of the cross-section of the post-hydration treated specimen disclosed the formation of a nanovoids-dispersed layer between the dielectric layer and the hydrated alumina layer. The nanovoids-dispersed layer contained a reduced amount of polymer, so this layer is likely to be more resistive. Re-anodizing to convert the nanovoids-dispersed layer to a dielectric layer reduced the breakdown voltage to ~500 V. Thus, it is confirmed that the formation of such nanovoids-dispersed layer with high resistivity plays an important role in enhancing the breakdown voltage of the aluminum solid capacitors.Alkyl group-modified PEDOT:PSS conductive polymers were synthesized to control the crystallinity and conductivity. The crystallinity and conductivity of the PEDOT:PSS were successfully reduced by introducing the alkyl group, and we could confirm that the breakdown voltage of the capacitors was highly enhanced by using ethyl-PEDOT:PSS instead of commercial PEDOT:PSS. D. Quintero, H. Matsuya, M. Iwai, S. Kitano, K. Fushimi, H. Habazaki, ACS Appl. Mater. Interfaces, 16 (2024) 1737-1748. This study was supported in part by the MEXT-Program for Creation of Innovative Core Technology for Power Electronics (INNOPEL), Grant Number JPJ009777.

DC-DC Buck Converters with Quasi-Online Estimation of Filter Capacitor Equivalent Parameters

The article focuses on devising solutions for monitoring the condition of the filter capacitors of DC-DC converters. The article introduces two novel DC-DC buck converter designs that monitor the equivalent series resistance (ESR) and the capacitance of capacitors using a parameter observer (PO) and simple variable electrical networks (VEN). For the first scheme, the PO processes in real time the voltage at the capacitor terminals during a discharge-charge cycle. For the second scheme, the filtering is performed with two or more capacitors in parallel, and the PO processes the voltage at the terminals of each capacitor during two discharge processes without interrupting the filtering operation of the converter. The paper presents the principles and theoretical support on which the two schemes of DC-DC buck converters are based, design details regarding PO and VEN, as well as experiments performed with each of the schemes. In the experimental schemes, the PO is implemented with a microcontroller, and the parameters of some aluminum electrolytic filter capacitors are calculated in a real-time manner of about . The calculation accuracy of the equivalent capacity is very good. Regarding the calculation accuracy of the ESR, it is shown that it depends on the fulfillment of certain ratios between the VEN resistances, on the one hand, as well as between them and the ESR, on the other hand.

Cation Effect of Bio‐Ionic Liquid‐Based Electrolytes on the Performance of Zn‐Ion Capacitors

AbstractZn‐ion capacitors (ZICs) are emerging as promising energy storage devices due to their low cost. Currently, aqueous‐based electrolytes are primarily used in ZIC which have shown issues related to low Zn deposition/stripping efficiencies, and Zn dendrites formation, resulting in device failure. To overcome these issues and to develop environmentally benign energy storage devices, here we have studied bio‐ionic liquid electrolytes (bio‐ILs) in both symmetric and asymmetric capacitors. Choline acetate (ChOAc) and betaine acetate (BetOAc) in water were investigated as electrolytes for capacitors in the presence and absence of Zn salts. Spectroscopic analysis showed that Zn solvation in the electrolytes changes significantly with the change in cation which affects the electrochemical reactions and capacitor performance. Raman analysis showed the Zn complex formed in the case of ChOAc is [Zn(OAc)4]2− whereas for BetOAc is [Zn(OAc)5]3− thereby the Zn deposition/stripping in ChOAc‐based electrolyte is quite stable whereas in case of BetOAc, Zn deposition/stripping is unstable. In the ChOAc electrolyte, the Zn/activated carbon asymmetric cell showed a capacity of &gt;90 F g−1 at 0.1 A g−1 and a capacitance close to 40 F g−1 at 0.5 A g−1 with ∼82 % capacity retention after 3000 cycles, whereas BetOAc could only be used in symmetric cell capacitor. This study shows that bio‐ILs can be used as sustainable electrolytes in energy storage devices wherein the cation plays a significant role in the capacitor performance.

Investigation of laser sintering process parameters for anode foils in aluminium electrolytic capacitors considering temperature distribution

Abstract The anode foil is a critical component of aluminium electrolytic capacitors, with its performance directly impacting the overall quality of the capacitors. Currently, sintered anode foil with excellent bending resistance and high specific capacitance is considered an ideal material for capacitor manufacturing; however, research on its optimal sintering parameters remains insufficient. In this study, a three-dimensional temperature field model is developed within the Comsol Multiphysics (6.0) environment, accounting for the temperature dependence of aluminium. By varying laser power and scanning speed, the temperature distribution along the laser scanning trajectory is determined, facilitating the identification of optimal process parameters for laser sintering anode foils in electrolytic capacitors. Subsequent laser sintering experiments validate the accuracy of these parameters. The findings indicate that the peak temperature of the molten pool rises with increased laser power and decreased scanning speed. The optimal process parameters for laser sintering anode foils in electrolytic capacitors are a powder layer thickness of 50 μm, a laser power of 140 W, and a scanning speed of 0.05 m s−1. The specific capacitance of laser-sintered anode foil, formed at voltages of 375 V and 520 V, ranges from 0.847 to 1.157 μF cm−2 and 0.717 to 0.935 μF cm−2, respectively, when the particle size is between 3 and 4 μm. A specific capacitance of 0.733 μF cm−2 can be achieved, which meets the performance requirements for aluminium electrolytic capacitors.

Design and analysis of power decoupling based microinverter considering parasitic parameters

With fossil energy reducing year by year, more and more attention to the new energy sources greatly promotes the development of the distributed power generation system, especially the low-power photovoltaic system. However, the power injected into the single-phase grid is time-varying, an electrolytic capacitor with large bulk should be paralleled with PV to balance the input and output power ripple. But the electrolytic capacitor has a very short lifetime, which could shorten the whole inverter’s lifetime. In this paper, the operational principle of the power decoupling based microinverter considering parasitic parameters is proposed, in which a film capacitor with small capacitance value replaces the electrolytic capacitor to improve the lifetime of the inverter. Further, the operating mode of the transformer and the decoupling capability is analyzed, and obtains the reasons affecting the inverter steady-state performance. Finally, the simulation and experiment validation of the proposed microinverter have been accomplished. Base on the analysis method proposed in this paper, a more accurate device selection can be provided for industrial design.

Carbon nanostructures for high-frequency line-filtering supercapacitors

Supercapacitors (SCs) are considered one of the front-runner energy storage devices for future electronic and automobile device applications. Even though their high-power densities, fast charge/discharge, and long cycling stabilities make them promising for future applications, their charge-discharge takes place below 1 Hz, a major issue for using them as capacitors for line filtering applications. Therefore, developing ultrafast electrochemical supercapacitors with alternating current (AC) line filtering functions has gained research attention to replace conventional aluminum electrolytic capacitors (AEC). Most available SCs possess resistive features rather than capacitive at 120 Hz because of the electrode geometry and configurations, which is a bottleneck in the research of line-filtering SCs. Addressing this challenge could be possible by developing novel electrode materials using hybrid nanostructures to meet the critical requirements for line filtering functions. This mini-review focuses on the advancement and challenges of carbon nanostructure-based electrode materials for AC line filtering applications and the future directions of this growing research area.

Modeling Systems with Dependent Catastrophic and Degradation Failures Incorporating Uncertainty

This research examines the interval-valued availability and cost of a competing-risk system with dependent catastrophic and degradation failures incorporating uncertainty. Uncertainty indicates that the probability of the successful operation of the system is not precisely known. The considered system has three states: normal, degraded, and totally failed. While degradation failures lessen the system’s overall effectiveness and lead it to a degraded state, a catastrophic failure abruptly terminates the system’s operations and results in a totally failed state. The interrelationship between these two failures is illustrated by the fact that each degradation failure elevates the possibility of a catastrophic failure. To identify a failure, sequential inspections are performed on the system. If the system is found to be degraded, a minimal repair is executed. If a catastrophic failure is detected, a corrective repair is performed. By integrating the aforesaid points, a theorem describing the upper and lower limits of the model’s reliability is derived. Furthermore, some theorems defining the bounds of point availability, long-run availability, and the average long-run cost rate are established. A numerical example of an aluminum electrolytic capacitor is taken to demonstrate the results.

Atomic doping of Alumina-based dielectric with high permittivity and breakdown field strength

High specific capacitance anode aluminum foils fabricated by introducing TiO2 to improve the permittivity (εr) of Al2O3 is one of the most effective ways to reduce the size and weight of aluminum electrolytic capacitors (AECs). However, the underlying mechanism by which the introduction of TiO2 causes capacity enhancement remains unclear. Here, a proposition is claimed that TiO2 is not directly responsible for the capacity enhancement but Al-doping TiO2 (AOT) actually. An atomically doping strategy based on atomic thermal diffusion and ionic electromigration is proposed to realize the fabrication of AOT via modulating the thermal and electric fields. Results show that the doping behavior of Al3+ induces the displacement of neighboring Ti4+ ions, which enhances the dipole polarization resulting in an increase of εr (25). Meanwhile, the diffusion of O2 and migration of O2– effectively removes the oxygen vacancy, enhancing the breakdown field strength (> 6 MV·cm−1) of dielectrics. Ultimately, the specific capacitance of anode foils is increased by about 50 % compared to those without AOT. On a brighter note, this work deepens the understanding of the capacity enhancement mechanism and will contribute to further facilitating the miniaturization of AECs.

Dual‐Phase Enabled Sinusoidal Current Anodizing for Efficient Preparation of High Specific Capacitance Anode Aluminum Foils

The anodized aluminum oxide prepared by anodizing is the core of aluminum electrolytic capacitors, and its quality determines the performance of aluminum electrolytic capacitors. The traditional direct current (t‐DC) anodizing method commonly used in industrial production today with low current density has the problems of low anodizing efficiency, poor crystallinity, and high formation constants of the oxide film. However, high current density direct current anodizing has the problems of severe defects of the oxide film and much thermal dissolution of aluminum foil. Herein, the dual‐phase enabled sinusoidal current (DESC) anodizing method is proposed for the preparation of 200 V anodized aluminum foil with much higher efficiency and performance. After testing, it is found that the alumina prepared by the DESC method has higher crystallinity and fewer defects. Consequently, the specific capacitance of the DESC sample is 23% greater than that of the t‐DC anodized sample, while the former displays a lower loss angle tangent and leakage current. Meanwhile, DESC anodizing takes 60% time less than t‐DC anodizing due to its high current density. The DESC anodizing method has been identified as a promising avenue for further investigation, exhibiting high efficiency and performance.