Al Electrolytic Capacitor Research Articles

Performance and Properties of a Ti-Al Composite Anodic Oxide Film on AC-Etched Al Foil

AC-etched aluminum foils for an Al electrolytic capacitor were covered with a TiO2 film by a sol–gel coating and then anodized to 25 V in an ammonium adipate solution. The structure, properties, and performance of the anodic oxide films were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), electrochemical impedance measurements (EIS), a general digital LCR meter, a TV characteristic tester, and multicycle pulse charging–discharging. It was found that the anodizing of aluminum coated with TiO2 films led to the formation of Al-Ti composite anodic oxide films, which consist of an outer Al-Ti composite oxide layer and an inner Al2O3 layer on the metal substrate. The capacitance (C25V) of the anodic oxide films formed on specimens with a TiO2 coating was about 10% larger than without a TiO2 coating. The specific resistance (Rox) of the Al-Ti composite film measured by EIS was lower than the blank one, accounting for a greater increase in the rise time (Tr) and a slight reduction in the withstand voltage (Vt). After hydration and a multicycle pulse charging–discharging destructive test, the Al-Ti composite anodic oxide film maintained the same good, comprehensive dielectric properties and performance as the blank one, thereby proving to be promising for acting as dielectric layers.

Overcoming voltage fluctuation in electric vehicles by considering Al electrolytic capacitor-based voltage stabilizer

Battery pack used in electrical vehicles (EVs) have developed fastly nowadays and are important due to its capability to stores electric charge. However, it is still found that there is an electrical voltage fluctuations due to sudden load changes or faults in the power system. To overcome this problem, the conventional strategy focuses on using voltage stabilizer with inductor-capacitor resonant circuits, leaving the problem of using capacitors at cryogenic temperatures. Herewith, we design a vehicle automatic voltage stabilizer (VAVS) operating at room temperature. The VAVS consists of nine main components, including resistors, capacitors, transistors, and diodes arranged with a specific composition to stabilize the voltage. By considering Al electrolytic capacitor, type of diode, resistor, and transistor, the VAVS device stabilizes the input voltage from 10-15V to obtain an output voltage of 12V. Then, by varying the engine rotation speed of vehicle, VAVS applied in vehicle battery supplies a constant voltage of about 12.1 V. The lowest line regulation analysis reveals a regulated voltage fluctuation of 0.17%/V. Our result shows that VAVS design works at room temperature, overcomes the voltage fluctuation and complies with the standard regulation of voltage stabilizers.

Analysis and Optimization of Electrolytic Capacitor Technology for High-Frequency Integrated Inverter

An increasing demand of electronic components suitable for high-speed switching in automotive applications has driven the development of high-frequency dc-link capacitors. Aluminum (Al)-electrolytic capacitors symbolize a promising, high-energy-density capacitor technology suitable for low-cost high-voltage automotive applications. However, the parasitic elements still represent a technological barrier of Al-electrolytic capacitors. In order to develop a novel capacitor, this article aims to develop guidelines for Al-electrolytic capacitors with reduced parasitic elements. This article concludes with the introduction of an automotive inverter concept, which benefits from the developed capacitors.

Intumescent fire retardant coating with recycled powder from industrial effluent optimized using response surface methodology

With the rapid development of Al electrolytic capacitors, plenty of industrial effluents are generated during the corrosion process of aluminium anode, resulting in serious environmental problems. To address such a challenging but urgent issue, we recycle powders containing lots of flame-retardant compositions from the precipitate of industrial effluents and apply them in the intumescent fire retardant coating. The formula of coating is optimized using response surface methodology based on central composite design. Under the optimum formula (APP: 60 wt%, PER: 19 wt%, MEL: 18 wt%, and the recycled powder: 9 wt%), the optimal sample is prepared and its fire resistance is investigated in our lab. During the fire resistance test, this sample displays the lowest backside temperature (only 163 °C) among all samples, indicating superior fire retardancy. In addition to fire resistance analysis, the water resistance and thermal stability of intumescent fire retardant coatings are also characterized. Our results show that the water contact angle and char yield of optimal sample reach up to 78.9° and 30.1 %, respectively. Thus, the optimal coating features superior fire retardancy, excellent water resistance and outstanding thermal stability. This work offers a practical strategy for creating a high-performance intumescent fire retardant coating based on the reuse of industrial effluent, which is favorable to environment protection and has a promising future in the industry.

Stacked High Voltage Al Electrolytic Capacitors Using Zr-Al-O Composite Oxide

A stacked high-voltage (900 V) Al electrolytic capacitor made with ZrO2 coated anode foils, which has not been studied so far, is realized and the effects of Zr-Al-O composite layer on the electric properties are discussed. Etched Al foils coated with ZrO2 sol are anodized in 2-methyl-1,3-propanediol (MPD)-boric acid electrolyte. The anodized Al foils are assembled with stacked structure to prepare the capacitor. The capacitance and dissipation factor of the capacitor with ZrO2 coated anode foils increase by 41 % and decrease by 50 %, respectively, in comparison with those of Al anode foils. Zr-Al-O composite dielectric layer is formed between separate crystalline ZrO2 with high dielectric constant and amorphous Al2O3 with high ionic resistivity. This work suggests that the formation of a composite layer by coating valve metal oxide on etched Al foil surface and anodizing it in MPD-boric acid electrolyte is a promising approach for high voltage and volume efficiency of capacitors.

Preparation of Nb2O5-Al2O3 Composite Anodic Oxide Film for an Aluminum Electrolytic Capacitor by Electrodeposition-Annealing and Anodization

Nb was electrodeposited on etched aluminum foils for an Al electrolytic capacitor. After annealing at 500°C in air, the foils were anodized in H3BO4 solution at 530 V to form Nb2O5-Al2O3 composite anodic oxide film as a dielectric layer. The voltage–time variations during the anodization process were monitored. The structure, composition, and electrical properties of the anodized foils were investigated by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and electrochemical impedance spectroscopy. The obtained foils were assembled into aluminum electrolytic capacitors, and the capacitor performance was tested according to the Japanese Nichicon standard. It was found that after electrodeposition and annealing, the slope of the voltage–time curve of the aluminum foil became steeper during the anodization process. The composite anodic oxide film showed a triple-layer structure consisting of Nb2O5/Al-NbOx/Al2O3 layers. The specific capacitance (C and Cox) of the composite anodic film was about 14% greater than that of the aluminum anodic oxide film. However, the leakage current (I) of the composite film was increased and its specific resistance (Rox) and withstanding voltage (Uw) decreased relative to the aluminum anodic oxide film, probably due to the greater number of intrinsic defects. During the load life and shelf life test, the composite anodic oxide film demonstrated capacitor performance similar to that of the aluminum anodic film, and can thus be used as a dielectric layer for capacitors to enhance specific capacitance.

Controllable Synthesis of Atomically Thin Type-II Weyl Semimetal WTe2 Nanosheets: An Advanced Electrode Material for All-Solid-State Flexible Supercapacitors.

Compared with 2D S-based and Se-based transition metal dichalcogenides (TMDs), Te-based TMDs display much better electrical conductivities, which will be beneficial to enhance the capacitances in supercapacitors. However, to date, the reports about the applications of Te-based TMDs in supercapacitors are quite rare. Herein, the first supercapacitor example of the Te-based TMD is reported: the type-II Weyl semimetal 1Td WTe2 . It is demonstrated that single crystals of 1Td WTe2 can be exfoliated into the nanosheets with 2-7 layers by liquid-phase exfoliation, which are assembled into air-stable films and further all-solid-state flexible supercapacitors. The resulting supercapacitors deliver a mass capacitance of 221 F g-1 and a stack capacitance of 74 F cm-3 . Furthermore, they also show excellent volumetric energy and power densities of 0.01 Wh cm-3 and 83.6 W cm-3 , respectively, superior to the commercial 4V/500 µAh Li thin-film battery and the commercial 3V/300 µAh Al electrolytic capacitor, in association with outstanding mechanical flexibility and superior cycling stability (capacitance retention of ≈91% after 5500 cycles). These results indicate that the 1Td WTe2 nanosheet is a promising flexible electrode material for high-performance energy storage devices.

Preparation of carbon nanotubes on Al foil anode for electrolytic capacitor

Well graphitized carbon nanotubes (CNTs) were directly grown on Al foil for Al electrolytic capacitor by micro-arc discharge in water between catalyst deposited Al foil cathode and Pt anode. Next, aluminum was sputtered onto the Al foil with grown CNTs at fixed sputtering time and power. Finally, aluminum oxide was formed by anodizing in an ammonium adipate solution. A high capacitance was obtained, comparing with blank Al foil without CNTs. High-resolution transmission electron microscopy and Raman spectra were employed to study the structure and formation mechanism of CNTs.

Electrolytic capacitors from the postwar period to the present

The first article in this series [1] covered the early history of electrolytic capacitors, from their invention around 1880 to the invention of the modern Al electrolytic capacitor structure in 1925. The second article [2] takes us from Samuel Ruben's 1925 invention to the wide range of Al electrolytic capacitors presently on the market. The present article discusses electrolytic capacitors based on metals other than Al.

Effect of Al2O3-ZrO2 Composite Oxide Thickness on Electrical Properties of Etched Al Foil

To increase the capacitance of an Al electrolytic capacitor, the anodic oxide film, Al2O3, was partly replaced by an Al2O3-ZrO2 (Al-Zr) composite film prepared by the vacuum infiltration method and anodization. The microstructure and composition of the prepared samples were investigated by scanning electron microscopy and transmission electron microscopy. The coated and anodized samples showed multi-layer structures, which consisted of an inner Al hydrate layer, a middle Al- Zr composite layer, and an outer Al2O3 layer. The thickness of the coating layer could go up to 220 nm when the etched Al foil was coated 8 times. The electrical properties of the samples, such as specific capacitance, leakage current, and withstanding voltages, were also characterized after anodization at 100 V and 600 V. The capacitances of samples with ZrO2 coating were 36.3% and 27.5% higher than those of samples without ZrO2 coating when anodized at 100 V and 600 V, respectively.

Lithographically Integrated Microsupercapacitors for Compact, High Performance, and Designable Energy Circuits

A wafer-scale integrated energy device circuit (IEDC) consisting of electrochemically isolated microsupercapacitor cells that could be connected in parallel and in series, as well as in arbitrarily arrangements. Such an IEDC possesses the same capacitance, operational voltage, and order relaxation time constant, although it is 1/1000th-times smaller than an equivalent Al electrolytic capacitor.

Enlargement of surface area of Al by electrochemical insertion and deinsertion of Li

Abstract Enlargement of the surface area of Al foils was carried out through the electrochemical insertion and deinsertion of Li. The electrochemical insertion and deinsertion of Li generated a fine porous structure on the surface of the Al foils. The specific surface area increased with the number of insertion and deinsertion cycles of Li and reached 300. This process can be applied to the effective enlargement of the surface area of Al foils, which is essential for increasing the capacitance of Al electrolytic capacitors.

The modern era of aluminum electrolytic capacitors

The first article in this series [1] covered the early history of electrolytic capacitors, from their invention around 1880 to the invention of the modern Al electrolytic capacitor structure in 1925. To summarize the early history, valve metals were recognized in the 1880s for their ability to conduct in one direction but impede current flow in the opposite direction as a result of oxide growth when submersed in an appropriate electrolyte. Early attempts to use the oxide as a dielectric so formed were frustrated by acidic electrolytes, which damaged the oxide layer and resulted in short capacitor life. Charles Pollak, a manufacturer of rechargeable batteries, realized the importance of the electrolyte and found that a neutral or basic electrolyte provides much greater stability of the oxide layer. In his 1896 German patent application for an electrolytic capacitor, Pollak described his invention as a liquid condenser with aluminum electrodes, which are covered with a uniformly insulating layer generated by forming with a weak current, characterized by using an alkaline or neutral electrolyte. Since the insulating layer is very thin, the condenser has a very high capacitance and could be used as a polarized capacitor in a DC circuit. Early electrolytic capacitors consisted of an Al electrode in a of electrolyte. The resistance of the electrolyte resulted in a relatively high equivalent series resistance (ESR), and the capacitors were both bulky and heavy, although not relative to the alternatives at the time. Mains-operated radio receivers, introduced around 1927, created a large consumer market for capacitors, which were required to produce ripple-free DC voltages. Wax paper capacitors, limited to 1 or 2 μF, had to be combined with bulky chokes (inductors) to produce efficient power frequency filters. Electrolytic capacitors provided much greater capacitance so that the chokes were not necessary, but early electrolytic capacitors used in radio receivers still consisted of an oxidized anode in a bath of electrolyte.

Effect of Environment on Sn Whisker Growth during Welding of Electronic Wires

In Pb-free Al-Sn welding of electrolytic parts, single-crystal Sn whiskers easily form and can cause problems such as short circuits. Here we report that the growth of Sn whiskers in the weld zone of Al electrolytic condenser leads was suppressed in a vacuum environment. We examined the effect of the environment and weld metal microstructure in order to understand how to control and prevent whisker growth. In vacuum, the weld zone did not form whiskers after more than 100 h, whereas in air, whiskers grew within several hours. This suggests that whiskers require oxygen to form. The growth can be explained by the energy balance between the potential energy of the weld metal and the surface energy of the whisker. Our results will contribute to developing techniques for suppressing the formation of Sn whiskers during the percussion welding of Al electrolytic capacitor leads.

Carbon nanosheet buckypaper: A graphene-carbon nanotube hybrid material for enhanced supercapacitor performance

Carbon nanosheets (CNS) are a graphene-based material with unique properties to improve both the speed and energy storage capability of electrochemical capacitors. In this study we employ CNS to demonstrate the fastest known response time of any electrochemical capacitor, with a turn-on frequency of 36 kHz exceeding that of Al electrolytic capacitors. Further we introduce a new hybrid material, “CNS-buckypaper”, i.e. CNS deposited onto freestanding buckypaper made from single-walled carbon nanotubes. Conformal deposition was achieved on ∼3 μm diameter nanotube bundles (or ropes) along the surface of the buckypaper which enabled a significant (∼4×) improvement in specific capacitance (from 60 to 230 F g−1) compared to as-produced buckypaper. We also discuss the synthesis, characterization, and integration of ultra-fast CNS-Ni current collectors and CNS-buckypaper electrodes into single and multi-cell supercapacitor devices. The packaged devices show high pulse-power performance at moderate energy density (∼1 Wh kg−1 at 22 kW kg−1) indicating potential for insertion into double-layer capacitor markets.

Effect of chemical plating Zn on DC-etching behavior of Al foil in HCl–H2SO4

The Al foil for high voltage Al electrolytic capacitor usage was immersed in 5.0% NaOH solution containing trace amount of Zn2+ and Zn was chemically plated on its surface through an immersion–reduction reaction. Such Zn-deposited Al foil was quickly transferred into HCl–H2SO4 solution for DC-etching. The effects of Zn impurity on the surface and cross-section etching morphologies and electrochemical behavior of Al foil were investigated by SEM, polarization curve (PC) and electrochemical impedance spectroscopy (EIS). The special capacitance of 100 V formation voltage of etched foil was measured. The results show that the chemical plating Zn on Al substrate in alkali solution can reduce the pitting corrosion resistance, enhance the pitting current density and improve the density and uniform distribution of pits and tunnels due to formation of the micro Zn–Al galvanic local cells. The special capacitance of etched foil grows with the increase of Zn2+ concentration.

AC–DC Converter Based on Parallel Drive of Two Piezoelectric Transformers

An AC–DC converter based on a parallel drive of two piezoelectric ceramic transformers was investigated. The transformers operate in a fundamental contour extensional vibration mode which has a large electromechanical coupling factor notwithstanding the use of a piezoelectric transversal effect. The converter includes Al electrolytic capacitors for smoothing circuits and metal oxide semiconductor field effect transistors (MOSFETs) for the switching and rectifying circuits. Maximum converter efficiency of 90% was obtained. The prospect of a low profile, highly efficient and high power (more than 50 W) AC–DC converter with piezoelectric transformers has been obtained through these experimental results.

Development of Dielectric Ceramics for Nickel Electrode Multilayer Capacitors

Calcium-doped BaTiO3-based dielectrics have a high resistance to reduction. This can be explained by taking the following three factors into account: 1) decrease in conduction electron density caused by acceptor Ca ions at the Ti site, 2) low freezing temperature of the equilibrium reaction by Ca ions at the Ti site, and 3) large enthalpy change in the reduction reaction by Ca ions at the Ba site. Fine-grained BaTiO3 ceramics can be prepared using the tetragonal BaTiO3 powder using ultra-fine starting BaTiO3 powder synthesized by hydrolysis method. The non-uniform distortion is caused in the grains during sintering, which is attributed to the surface tension and clamping stress from the thin grain boundary layer. This suppresses the tetragonality symmetry of the grains and provides the BaTiO3 ceramics with a high dielectric constant, low loss, and flat capacitance temperature characteristics. The Ca-doped ultra-thin dielectric layer compatible with nickel electrode can realize the nickel electrode multilayer capacitors of large capacitance and large volumetric efficiency, which is competitive with the Ta and Al-electrolytic capacitors and as reliable as conventional precious metal electrode multilayer capacitors.

Study on sintered anodes of Nb–Ta–Al aluminothermic alloys

This work presents the results of a study concerning the morphological and electrical properties of sintered anodes of Nb–Ta–Al aluminothermic alloys. These alloys have potential application in electrolytic capacitors. The compacting behavior of the Nb–Ta–Al powders was evaluated during uniaxial pressing in a steel die. Anodes with a low green density (compacting pressure below 60 MPa) were sintered in vacuum ( ∼10 −4 Pa) at temperatures between 1300 and 1600°C for 15, 40 and 60 min. Significant changes of the morphological and electrical properties occurred during sintering. The Nb–Ta–Al electrolytic capacitors gave high specific charge from 14310 to 27807 μ FV/g.

Application to electronic devices using organic thin films by ion-beam-evaporation method

Among various methods for preparation of organic thin films, we proposed an ion implantation technique using positive ion beams of low energy under 50 ~ 100 eV. The Al electrolytic capacitor with charge transfer complex as solid electrolyte, the electroluminescent (EL) diode with double-layer structure (Mg:In/Alq 3/TPD/ITO) and the solar cell with Schottky junction or heterojunction of organic thin films were prepared by this method. The solid electrolytic capacitor with a good high frequency response of impedance was obtained to use the evaporated films. The light emission intensity and the life time of EL diodes were higher and longer than that of the conventional thermal deposition method. The conversion efficiency of the solar cells was 1.2 % in the case of Schottky structure (Al/CuPc/ITO) with the phthalocyanine compounds.