Sustainable and Printable Nanocellulose-Based Ionogels as Gel Polymer Electrolytes for Supercapacitors

A new gel polymer electrolyte (GPE) based supercapacitor with an ionic conductivity up to 0.32–0.94 mS cm−2 has been synthesized from a mixture of an ionic liquid (IL) with nanocellulose (NC). The new NC-ionogel was prepared by combining the IL 1-ethyl-3-methylimidazolium dimethyl phosphate (EMIMP) with carboxymethylated cellulose nanofibers (CNFc) at different ratios (CNFc ratio from 1 to 4). The addition of CNFc improved the ionogel properties to become easily printable onto the electrode surface. The new GPE based supercapacitor cell showed good electrochemical performance with specific capacitance of 160 F g−1 and an equivalent series resistance (ESR) of 10.2 Ω cm−2 at a current density of 1 mA cm−2. The accessibility to the full capacitance of the device is demonstrated after the addition of CNFc in EMIMP compared to the pristine EMIMP (99 F g−1 and 14.7 Ω cm−2).

DC-Link Capacitor Diagnosis in a Single-Phase Grid-Connected PV System

The DC-link capacitor is one of the components that are more prone to faults in energy-distributed systems based on voltage source inverters. A predictive maintenance approach should allow to foresee the risk of an unexpected system shutdown. In this study, a two-stage diagnostic approach that is aimed at determining the health status of the DC-link capacitor in a single-phase grid-connected PV system was proposed. The equivalent series resistance (ESR) and the capacitance (C) values were used as indicators in the estimation of the degradation stage. Electrochemical impedance spectroscopy (EIS) was used to estimate the impedance curve of the DC-link capacitor, and a multi-fitting algorithm allowed us to determine the ESR and C parameters. A comparison between the estimated values C and ESR and the nominal values was used to quantify the fault severity. It was demonstrated that the EIS allowed the determination of the capacitor impedance regardless of the actual operating conditions of the photovoltaic generator, such as during irradiance changes and with the maximum power point algorithm turned off. By using the capacitor simplified model and a multi-fitting algorithm, the C and ESR values were estimated with an error that was lower than 1%. An analysis of the hardware required to implement the proposed approach in real applications by achieving the desired accuracy was also proposed.

Effect of High Temperature Storage on AC Characteristics of Polymer Tantalum Capacitors

Replacement of MnO2 with conductive polymers as cathode materials in chip tantalum capacitors allows for a substantial reduction of the equivalent series resistance (ESR), improvement of frequency characteristics, and elimination of the possibility of ignition during failures. One of the drawbacks of chip polymer tantalum capacitors (CPTCs) is a relatively poor long-term stability at high temperatures. In this work, variations of capacitance, dissipation factor, and ESR in different types of capacitors including automotive grade parts from three manufacturers have been monitored during storage at temperatures from 100°C to 175°C for up to 18,000 h. Results show that ESR is the most and capacitance the least sensitive to degradation parameter. Times to parametric failures have been simulated using a Weibull-Arrhenius model that allowed for assessments of activation energies of the degradation and prediction of times to failure at the use temperature. Degradation of CPTCs was explained by thermo-oxidative processes in conductive polymers that result in exponential increasing of the resistivity with time of ageing. This process starts after a certain incubation period that depends on packaging materials and design and corresponds to the time that is necessary to form delamination between the encapsulating molding compound and lead frame. The effectiveness of the existing qualification procedures to assure stable operation of CPTCs is discussed.

Electrospun flexible lignin/polyacrylonitrile-based carbon nanofiber and its application in electrode materials for supercapacitors

In this study, a lignin/polyacrylonitrile (PAN) composite nanofiber membrane is prepared by electrospinning and used as the precursor to prepare flexible carbon nanofibers (CNFs) through pre-oxidation and carbonization. The micromorphology, crystal structure, pore size distribution and specific surface area of the CNFs are characterized by field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and specific surface adsorption analysis, respectively. The electrochemical properties of the CNF membrane are also investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy due to its potential application in binder-free electrode materials for supercapacitors. We successfully prepared flexible CNFs with an average diameter of about 539 nm and a specific surface area of 1053.78 m2/g when the mass ratio of lignin to PAN was 9:1 in a solution concentration of 28 wt%. The CNFs are loaded onto nickel foam to prepare the electrode materials for supercapacitors without a binder. When the current density is 0.5 A/g, the specific capacitance could be up to 201.27 F/g and the equivalent series resistance is only 0.57 Ω, which shows an excellent electrochemical performance. This study not only provides a theoretical basis for the high-value utilization of lignin and the preparation of flexible lignin/PAN-based CNFs, but also provides a new type of environmentally friendly raw material for the electrodes of supercapacitors and could be helpful to alleviate the energy crisis and environmental pollution.

Novel Thermally Reduced Graphene Oxide Microsupercapacitor Fabricated via Mask—Free AxiDraw Direct Writing

We demonstrate a simple method to fabricate all solid state, thermally reduced Graphene Oxide (TRGO) microsupercapacitors (µ-SCs) prepared using the atmospheric pressure chemical vapor deposition (APCVD) and a mask-free axiDraw sketching apparatus. The Fourier transform infrared spectroscopy (FTIR) shows the extermination of oxygen functional groups as the reducing temperature (RT) increases, while the Raman shows the presence of the defect and graphitic peaks. The electrochemical performance of the µ-SCs showed cyclic voltammetry (CV) potential window of 0–0.8 V at various scan rates of 5–1000 mVs−1 with a rectangular shape, depicting characteristics of electric double layer capacitor (EDLC) behavior. The µ-SC with 14 cm−2 (number of digits per unit area) showed a 46% increment in capacitance from that of 6 cm−2, which is also higher than the µ-SCs with 22 and 26 cm−2. The TRGO-500 exhibits volumetric energy and power density of 14.61 mW h cm−3 and 142.67 mW cm−3, respectively. The electrochemical impedance spectroscopy (EIS) showed the decrease in the equivalent series resistance (ESR) as a function of RT due to reduction of the resistive functional groups present in the sample. Bode plot showed a phase angel of −85° for the TRGO-500 µ-SC device. The electrochemical performance of the µ-SC devices can be tuned by varying the RT, number of digits per unity area, and connection configuration (parallel or series).

Adaptive On-Time Buck Converter with Wave Tracking Reference Control for Output Regulation Accuracy

A ripple-based constant on-time (RBCOT) buck converter with a virtual inductor current ripple (VICR) control can relax the stability constraint of large equivalent series resistance (ESR) at an output capacitor, but output regulation accuracy deteriorates due to the issue with output DC offset. Thus, this paper proposes a wave tracking reference (WTR) control to improve converter stability with low ESR and concurrently eliminate output DC offset on the regulated output voltage. Moreover, an adaptive on-time (AOT) circuit is presented to suppress the switching frequency variation with load current changes in continuous conduction mode. A prototype chip was fabricated in 0.35 µm CMOS technology for validation. The measurement results demonstrate that the maximum output DC offset is 4.1 mV and the output voltage ripple is as small as 3 mV. Furthermore, the switching frequency variation with the AOT circuit is 11 kHz when load current changes from 50 mA to 500 mA, and the measured maximum efficiency is 90.9% for the maximum output power of 900 mW.

Evolution of Polymer Tantalum Capacitors

The major advantage of Polymer Tantalum capacitors over other types of tantalum capacitors is their low equivalent series resistance (ESR), providing a higher capacitance stability with frequency and ripple current capability. When Polymer Tantalum capacitors were introduced to the market in mid 1990s, they were low voltage, leaky, and unreliable, which limited their applications to commercial electronics. Today, some types of polymer tantalum capacitors demonstrate the highest working voltage, lowest DC leakage, and highest reliability ever achieved in tantalum capacitors. These Polymer Tantalum capacitors combine outstanding performance and reliability with superior volumetric charge efficiency, which makes them cost effective and attractive for numerous applications, including mission critical ones. This paper is dedicated to the major technological breakthroughs and scientific discoveries that enabled the radical evolution of Polymer Tantalum capacitors.

Comparative Investigation of Non-halogenated Imidazolium and Phosphonium-based Surface-Active Ionic Liquids as Electrolyte for Supercapacitors

<p>We report a comparative analysis of non-halogenated surface-active ionic liquids (SAILs), which consists of the surface-active anion, 2-ethylhexyl sulfate, and the phosphonium, and imidazolium cations <i>i.e.,</i> tetrabutylphosphonium ([P₄₄₄₄]⁺), trihexyl(tetradecyl)phosphonium ([P₆₆₆₁₄]⁺), and 1-methyl-3-hexylimidazolium ([C₆C₁IM]⁺). We explored the thermal and electrochemical properties, <i>i.e.</i>, degradation, melting and crystallization temperatures, and ionic conductivity of this new class of IL. These SAILs were tested as an electrolyte in a multi-walled carbon nanotubes (MWCNTs)-based supercapacitor at various temperatures from 253 to 373 K. The electrochemical performance of different SAILs by varying the cationic core as a function of temperature were compared, in the same MWCNT-based supercapacitor. We found that the supercapacitor cell with [C₆C₁IM][EHS] shown high specific capacitance (<i>C_elec</i> in F g^-1), a high energy density (<i>E</i> in Wh kg^-1), and a high power density (<i>P</i> in kW kg^-1) when compared to those for the other SAILs <i>i.e.</i> [P₄₄₄₄][EHS], [P₆₆₆₁₄][EHS], and [N₈₈₈₈][EHS] at all temperatures. The supercapacitor with an MWCNT-based electrode and [C₆C₁IM][EHS], [P₄₄₄₄][EHS], and [P₆₆₆₁₄][EHS] as an electrolyte showed a specific capacitance of 148, 90, and 47 F g^-1 (at the scan rate of 2 mV s^-1) with an energy density of 82, 50, and 26 Wh kg^-1 (at 2 mV s^-1) respectively, at 298 K. The temperature effect can be seen by the three to four-fold increase in the specific capacitance of the cell and the energy density values, <i>i.e.</i>, 290, 198, and 114 F g^-1 (at 2 mV s^-1) and 161, 110, and 63 Wh kg^-1 (at 2 mV s^-1), respectively, at 373 K. This study reveals that these new SAILs specifically [C₆C₁IM][EHS] and [P₄₄₄₄][EHS] can potentially be used as electrolytes in the wide range of temperature. The solution resistance (<i>R_s</i>), charge transfer resistance (<i>R_ct</i>), and equivalent series resistance (ESR) also decreased with an increase in temperature for all SAILs as electrolytes. These new SAILs can explicitly be used for high-temperature (wide range of temperature) electrochemical applications, such as efficient supercapacitors for high energy storage due to enhanced specific capacitance, energy, and power density at elevated temperatures. </p>

Comparative Investigation of Non-halogenated Imidazolium and Phosphonium-based Surface-Active Ionic Liquids as Electrolyte for Supercapacitors

<p>We report a comparative analysis of non-halogenated surface-active ionic liquids (SAILs), which consists of the surface-active anion, 2-ethylhexyl sulfate, and the phosphonium, and imidazolium cations <i>i.e.,</i> tetrabutylphosphonium ([P₄₄₄₄]⁺), trihexyl(tetradecyl)phosphonium ([P₆₆₆₁₄]⁺), and 1-methyl-3-hexylimidazolium ([C₆C₁IM]⁺). We explored the thermal and electrochemical properties, <i>i.e.</i>, degradation, melting and crystallization temperatures, and ionic conductivity of this new class of IL. These SAILs were tested as an electrolyte in a multi-walled carbon nanotubes (MWCNTs)-based supercapacitor at various temperatures from 253 to 373 K. The electrochemical performance of different SAILs by varying the cationic core as a function of temperature were compared, in the same MWCNT-based supercapacitor. We found that the supercapacitor cell with [C₆C₁IM][EHS] shown high specific capacitance (<i>C_elec</i> in F g^-1), a high energy density (<i>E</i> in Wh kg^-1), and a high power density (<i>P</i> in kW kg^-1) when compared to those for the other SAILs <i>i.e.</i> [P₄₄₄₄][EHS], [P₆₆₆₁₄][EHS], and [N₈₈₈₈][EHS] at all temperatures. The supercapacitor with an MWCNT-based electrode and [C₆C₁IM][EHS], [P₄₄₄₄][EHS], and [P₆₆₆₁₄][EHS] as an electrolyte showed a specific capacitance of 148, 90, and 47 F g^-1 (at the scan rate of 2 mV s^-1) with an energy density of 82, 50, and 26 Wh kg^-1 (at 2 mV s^-1) respectively, at 298 K. The temperature effect can be seen by the three to four-fold increase in the specific capacitance of the cell and the energy density values, <i>i.e.</i>, 290, 198, and 114 F g^-1 (at 2 mV s^-1) and 161, 110, and 63 Wh kg^-1 (at 2 mV s^-1), respectively, at 373 K. This study reveals that these new SAILs specifically [C₆C₁IM][EHS] and [P₄₄₄₄][EHS] can potentially be used as electrolytes in the wide range of temperature. The solution resistance (<i>R_s</i>), charge transfer resistance (<i>R_ct</i>), and equivalent series resistance (ESR) also decreased with an increase in temperature for all SAILs as electrolytes. These new SAILs can explicitly be used for high-temperature (wide range of temperature) electrochemical applications, such as efficient supercapacitors for high energy storage due to enhanced specific capacitance, energy, and power density at elevated temperatures. </p>

Bio-Based Plasticized PVA Based Polymer Blend Electrolytes for Energy Storage EDLC Devices: Ion Transport Parameters and Electrochemical Properties

This report shows a simple solution cast methodology to prepare plasticized polyvinyl alcohol (PVA)/methylcellulose (MC)-ammonium iodide (NH4I) electrolyte at room temperature. The maximum conducting membrane has a conductivity of 3.21 × 10−3 S/cm. It is shown that the number density, mobility and diffusion coefficient of ions are enhanced by increasing the glycerol. A number of electric and electrochemical properties of the electrolyte—impedance, dielectric properties, transference numbers, potential window, energy density, specific capacitance (Cs) and power density—were determined. From the determined electric and electrochemical properties, it is shown that PVA: MC-NH4I proton conducting polymer electrolyte (PE) is adequate for utilization in energy storage device (ESD). The decrease of charge transfer resistance with increasing plasticizer was observed from Bode plot. The analysis of dielectric properties has indicated that the plasticizer is a novel approach to increase the number of charge carriers. The electron and ion transference numbers were found. From the linear sweep voltammetry (LSV) response, the breakdown voltage of the electrolyte is determined. From Galvanostatic charge-discharge (GCD) measurement, the calculated Cs values are found to drop with increasing the number of cycles. The increment of internal resistance is shown by equivalent series resistance (ESR) plot. The energy and power density were studied over 250 cycles that results to the value of 5.38–3.59 Wh/kg and 757.58–347.22 W/kg, respectively.