Narrow Voltage Range Research Articles

Tracing Low Amounts of Mg in the Doped Cathode Active Material LiNiO2

The resurgence of electromobility drives the need for high energy density cathode materials. LiNiO2 (LNO) meets this demand, based on its high specific capacity in a narrow voltage range and without relying on scare elements. Yet, it has been plagued by various issues, such as poor cycling performance and thermal instability. Adding dopants, such as widely available Mg2+, is a common strategy to balance cycling performance and energy density. Most prior studies focused on large Mg content ranges and were based on laboratory X-ray diffraction. Hence, the influence of Mg2+ addition on the crystal structure remains ambiguous, especially when small amounts are used (≤ 5 mol%; particularly interesting for industrial applications). Here, we present a systematic study of LiNi1−y Mg y O2 (0 ≤ y ≤ 0.05) investigated by high-resolution synchrotron-based X-ray diffraction combined with elemental analysis, electron microscopy and electrochemical testing. The synthetic route relies on the addition of 10 nm Mg(OH)2 nanoparticles prior to the final calcination, as well as on co-precipitation. It is found that Mg2+ mostly occupies the Ni site until saturating at ∼1.7%, then the Li site becomes preferred. This trend in the site occupancies influences the lattice parameters, oxygen coordinate within the unit cell and Ni–O bond distances. Doping also modifies the electrochemical behavior as a cathode material, stabilizing the capacity retention during cycling but sacrificing specific discharge capacity. Laboratory-based operando X-ray diffraction reveals that the increase in capacity retention is due to the suppression of the H2-H3 phase transition and interlayer distance collapse already in 3% Mg-doped LNO. The combination of structural and electrochemical characterization of doped LNO provides useful insights into the structural chemistry of the Mg2+ dopant and can serve as a starting point to understand Mg as a component in multiple dopant strategies for cathode material design and application.

리튬이온 배터리의 랜덤 포레스트 기반 잔여 용량 추정 및 중요 전압 구간 선정 연구

This paper proposes random forest regression, which is an ensemble model for estimating the remaining battery capacity. The partial capacity of the set charging voltage range and the remaining capacity are used as the training data for the random forest model. The training data can be used directly without any pre-processing. When the partial capacity of a specific voltage range is entered into the trained random forest model, it estimates the remaining capacity. Furthermore, the important voltage range is extracted by selecting the voltage section that is critical for estimating the remaining capacity based on the permutation importance. The mean absolute error and coefficient of determination were used to validate the important voltage range. Validation results show that the proposed model can estimate the remaining capacity with a low error. Therefore, the proposed model can be used for online battery capacity estimation using a narrow voltage range.

Coupling aqueous zinc batteries and perovskite solar cells for simultaneous energy harvest, conversion and storage

Simultaneously harvesting, converting and storing solar energy in a single device represents an ideal technological approach for the next generation of power sources. Herein, we propose a device consisting of an integrated carbon-based perovskite solar cell module capable of harvesting solar energy (and converting it into electricity) and a rechargeable aqueous zinc metal cell. The electrochemical energy storage cell utilizes heterostructural Co2P-CoP-NiCoO2 nanometric arrays and zinc metal as the cathode and anode, respectively, and shows a capacity retention of approximately 78% after 25000 cycles at 32 A/g. In particular, the battery cathode and perovskite material of the solar cell are combined in a sandwich joint electrode unit. As a result, the device delivers a specific power of 54 kW/kg and specific energy of 366 Wh/kg at 32 A/g and 2 A/g, respectively. Moreover, benefiting from its narrow voltage range (1.40–1.90 V), the device demonstrates an efficiency of approximately 6%, which is stable for 200 photocharge and discharge cycles.

Body-Effect-Free OLED-on-Silicon Pixel Circuit Based on Capacitive Division to Extend Data Voltage Range

This paper proposes an OLED pixel compensation circuit that copes with threshold voltage variation, narrow data voltage range, and body effect on a backplane of silicon-based transistors. It consists of six PMOS transistors and two capacitors. The data voltage range is extended by the capacitor division with two capacitors, and the connection of both source and gate nodes to the supply voltage makes the driving transistor free from the body effect. In addition, the reference voltage is used to initialize the gate node voltage of the driving transistor as well as to adjust the data voltage region. By the SPICE simulation, it is verified that the current error over the threshold voltage variations of ±10 mV is reduced to be −1.200% to 0.964% at the maximum current range of around 8 nA, and the data voltage range is extended to 3.4 V, compared to the large current error range from −21.46% to 27.36% and the data voltage range of 0.41 V in the basic 2T1C circuit. In addition, the body-effect-free circuit outperforms the latest 4T1C circuit of the current error range from −3.279% to 3.388%.

Threshold behaviors of direct and Hall currents in topological spin-Hall effect

We study spin-dependent direct and Hall conductivities in the threshold region of Fermi energy, ɛF=2J, where J is the exchange integral between the conduction electron spins and the skyrmion spin texture. For ɛF at the threshold value and above the spin-down electrons are allowed to exist. We find the two in the direct and four narrow peaks in the Hall conductivities for Fermi energies slightly below the threshold value. The found effects are dramatic because the electric current changes by approximately eight times in the narrow range of gate voltages (∼4 meV). The values of the peaks strongly depend on skyrmion size. For small and very large skyrmion sizes the peak amplitudes are small compared to the conductivity absolute values. At the skyrmion radius a=6nm and very light conduction electrons, m∗∼10−2me, the extrema are the most pronounced. The temperature evolution reveals the strong smearing effect where the peak-wise behavior completely disappears at room temperatures. Spin transistor could be considered for possible applications where in the narrow region of gate voltage the sharp conductivity change occurs.

Controlling morphology, adhesion, and electrochromic behavior of PEDOT films through molecular design and processing

AbstractPoly(3,4‐ethylenedioxythiophene) (PEDOT) is a well‐known semiconducting polymer with favorable properties which find it often applied as the active material in biological sensors and electrochromic devices. However, PEDOT has several drawbacks which can prohibit its effective or long‐term use, including weak adhesion to substrates such as ITO‐coated glass, poorly controlled surface morphology, and reduced electrochemical stability over time. While a diverse range of approaches have been explored to overcome these issues, most involve additives or substrate modification, while solutions based on direct covalent adaptation are relatively lacking. We present a novel polymer based on covalently modified EDOT (PEDOT‐Crown), featuring polar motifs and a 15‐crown‐5 moiety. Compared to PEDOT, PEDOT‐Crown demonstrates a wealth of advantageous properties including: superior adhesion to ITO under physical and electrochemical duress; a more uniform surface morphology; and electrochemical properties including a higher contrast ratio, red‐shifted polaron and bipolaron absorption features, bleaching of the neutral absorption band across a narrower voltage range, and more Faradaic rather than capacitive behavior. Additionally, we note that in the presence of Na+, PEDOT‐Crown appears to show modified behavior in long‐term electrochemical experiments. These features make PEDOT‐Crown a material with improved suitability for application in biological sensing and electrochromic devices, compared to PEDOT.

Towards Reversible High-Voltage Multi-Electron Reactions in Alkali-Ion Batteries Using Vanadium Phosphate Positive Electrode Materials.

Vanadium phosphate positive electrode materials attract great interest in the field of Alkali-ion (Li, Na and K-ion) batteries due to their ability to store several electrons per transition metal. These multi-electron reactions (from V2+ to V5+) combined with the high voltage of corresponding redox couples (e.g., 4.0 V vs. for V3+/V4+ in Na3V2(PO4)2F3) could allow the achievement the 1 kWh/kg milestone at the positive electrode level in Alkali-ion batteries. However, a massive divergence in the voltage reported for the V3+/V4+ and V4+/V5+ redox couples as a function of crystal structure is noticed. Moreover, vanadium phosphates that operate at high V3+/V4+ voltages are usually unable to reversibly exchange several electrons in a narrow enough voltage range. Here, through the review of redox mechanisms and structural evolutions upon electrochemical operation of selected widely studied materials, we identify the crystallographic origin of this trend: the distribution of PO4 groups around vanadium octahedra, that allows or prevents the formation of the vanadyl distortion (O…V4+=O or O…V5+=O). While the vanadyl entity massively lowers the voltage of the V3+/V4+ and V4+/V5+ couples, it considerably improves the reversibility of these redox reactions. Therefore, anionic substitutions, mainly O2− by F−, have been identified as a strategy allowing for combining the beneficial effect of the vanadyl distortion on the reversibility with the high voltage of vanadium redox couples in fluorine rich environments.

High-performance 2.5 V aqueous asymmetric supercapacitor based on MnO2 nanowire/hierarchical porous carbon composite

ABSTRACT Aqueous supercapacitor shows a narrow operating voltage range because of the limitation of the water electrolysis, resulting in low energy density. In this work, a nanoporous MnO2 entangled hierarchical porous carbon skeleton (simplified to MHPC) has been successfully prepared. Aqueous asymmetric supercapacitor has been assembled by employing the MHPC as a positive electrode, a hierarchical porous carbon skeleton (HPC) as a negative electrode, and a neutral Na2SO4 aqueous solution as electrolyte. The assembled asymmetric supercapacitor can be stably charged in an aqueous medium in a wide voltage range of 0–2.5 V and delivers a maximum energy density of 20.8Wh/kg at a power density of 0.25 kW/kg and 25 kW/kg at an energy density of 11.1 Wh/kg in a 1 M Na2SO4 aqueous solution. This strategy provides a new idea for developing high-energy supercapacitor.

A New Approach for Power Losses Evaluation of IGBT/Diode Module

Electric power systems are facing tremendous changes and power electronic devices are playing an increasingly crucial role in this transformation. In this contest, the study of power electronic devices behavior becomes of the utmost importance, and in particular, evaluation of their losses to understand their performance. Several methods can be found in literature to evaluate power or energy losses, but each of them is associated with shortcomings (such as missing an important factor or having narrow current or voltage range) that in practice become a strong limit to implement them or in a simulation process. To overcome this problem, this paper evaluates existing methods and proposes new loss calculation methods for power electronics losses that can be used within simulation tools at any converter configuration and application range, splitting power electronic losses into switching and conduction losses. The proposed new approach formulates each loss calculation procedure in a systematic way. The presented methods are implemented in Matlab Simulink and simulation results are compared with data obtained from the Semikron SemiSel v4 online tool, which is used as a benchmark. The outcomes reveal that, with this new approach, the proposed methods can cover wider working operation range compared to the existing methods having better accuracy.

High-Efficiency LLC Resonant Converter With Reconfigurable Voltage Multiplying Rectifier for Wide Output Voltage Applications

This article presents a reconfigurable voltage multiplying rectifier (RVMR) to improve the performance of an LLC resonant converter for wide output voltage applications. The RVMR can operate as voltage-doubler mode or voltage-quadrupler mode according to the primary switching strategy. Two operation modes split a wide output voltage range into two narrow ranges. Therefore, the RVMR enables the LLC resonant tank to be designed in a narrow output voltage range, which results in a narrow switching frequency range, high efficiency, and high power density. A smooth mode transition can be achieved by adopting a phase-shift control to general pulse frequency modulation control without any additional switch. The proposed RVMR LLC converter can improve its efficiency by 2.9% and reduce component volume by 26% compared to the conventional full-bridge LLC resonant converter. A 750-W prototype with 400 V input, 100-300 V output voltage, and 2.5 A max output current has been built and tested to verify the effectiveness of the proposed converter.

Wide Voltage Resonant Converter Using a Variable Winding Turns Ratio

This paper presents a inductor–inductor–capacitor (LLC) resonant converter with variable winding turns to achieve wide voltage operation (100–400 V) and realize soft switching operation over the entire load range. Resonant converters have been developed for consumer power units in computers, power servers, medical equipment, and adaptors due to the advantages of less switching loss and better circuit efficiency. The main disadvantages of the LLC resonant converter are narrow voltage range operation owing to wide switching frequency variation and limited voltage gain. For computer power supplies with hold-up time function, electric vehicle battery chargers, and for power conversion in solar panels, wide input voltage or wide output voltage operation capability is normally demanded for powered electronics. To meet these requirements, the variable winding turns are used in the presented circuit to achieve high- or low-voltage gain when Vin is at low- or high-voltage, respectively. Therefore, the wide voltage operation capability can be implemented in the presented resonant circuit. The variable winding turns are controlled by an alternating current (AC) power switch with two back-to-back metal-oxide-semiconductor field-effect transistors (MOSFETs). A 500-W prototype is implemented and test results are presented to confirm the converter performance.

Mechanistic Investigation of a Hybrid Zn/V2 O5 Rechargeable Battery with a Binary Li+ /Zn2+ Aqueous Electrolyte.

Low-cost, easily processable, and environmentally friendly rechargeable aqueous zinc batteries have great potential for large-scale energy storage, which justifies their receiving extensive attention in recent years. An original concept based on the use of a binary Li+ /Zn2+ aqueous electrolyte is described herein for the case of the Zn/V2 O5 system. In this hybrid, the positive side involves mainly the Li+ insertion/deinsertion reaction of V2 O5 , whereas the negative electrode operates according to zinc dissolution-deposition cycles. The Zn//3 mol L-1 Li2 SO4 -4 mol L-1 ZnSO4/ //V2 O5 cell worked in the narrow voltage range of 1.6-0.8 V with capacities of approximately 136-125 mA h g-1 at rates of C/20-C/5, respectively. At 1 C, the capacity of 80 mA h g-1 was outstandingly stable for more than 300 cycles with a capacity retention of 100 %. A detailed structural study by XRD and Raman spectroscopy allowed the peculiar response of the V2 O5 layered host lattice on discharge-charge and cycling to be unraveled. Strong similarities with the well-known structural changes reported in nonaqueous lithiated electrolytes were highlighted, although the emergence of the usual distorted δ-LiV2 O5 phase was not detected on discharge to 0.8 V. The pristine host structure was restored and maintained during cycling with mitigated structural changes leading to high capacity retention. The present electrochemical and structural findings reveal a reaction mechanism mainly based on Li+ intercalation, but co-intercalation of a few Zn2+ ions between the oxide layers cannot be completely dismissed. The presence of zinc cations between the oxide layers is thought to relieve the structural stress induced in V2 O5 under operation, and this resulted in a limited volume expansion of 4 %. This fundamental investigation of a reaction mechanism operating in an environmentally friendly aqueous medium has not been reported before.

A carbon-based memristor design for associative learning activities and neuromorphic computing.

Carbon quantum dots (QDs) have attracted significant interest due to their excellent electronic properties and wide application prospects. However, the application of carbon QDs has been rarely reported in memristors. Here, a memristor model with carbon conductive filaments (CFs) is proposed for the first time based on carbon quantum dots. The CF-based devices exhibited excellent resistive switching performance, in particular a narrow range of SET and RESET voltages and good power efficiency and retention properties. These devices could also emulate important biological synapse performances, such as the transition from short-term plasticity (STP) to long-term potentiation (LTP) behaviors, long-term depression (LTD) behavior, and four types of spike-timing-dependent plasticity (STDP) learning rules. Interestingly, Pavlovian associative learning functions were also reliably demonstrated in the memristor device (MD). The digit recognition ability of the MDs was evaluated though a single-layer perceptron model, in which the recognition accuracy of digits reached 92.63% after 250 training iterations. The transmission electron microscopy (TEM) results evidenced that the carbon CF was found in the MD at the "ON" state. Thus, this new carbon CF-based mechanism for memristors provides a new idea for achieving better neuromorphic MDs and applications.

Adaptive‐stage rectifier for mm ‐scale implants

As the dimensions of neural implants are miniaturised to mm-scale, wireless powering becomes more challenging. Antenna sizes become smaller, and so does the amplitudes of the received RF signal. More importantly, a meticulous effort is required when multiple implants are placed on the brain under a transmitter, as each implant has a different spatial position from the transmitter coil. In addition, RF power may fluctuate over time. These factors, both effects the coupling coefficient. In this case, rectifiers with a fixed number of stages are limited to a rather narrow operational voltage range, and cannot accommodate such variations. To address this, the authors propose an adaptive-stage rectifier that changes the number of connected stages by monitoring the final rectifier output voltage using two comparators and a digital block. By doing so, it can generate an output voltage within the targeted voltage range for a much wider RF input voltage range. The authors' design and simulations in 180-nm CMOS SOI process show that the proposed rectifier is capable of keeping the output voltage within 1-1.7 V for an RF input range from 0.73 to 2 V, which is five times wider than that of conventional rectifiers with three fixed stages.

An aqueous symmetric supercapacitor based on Mn3O4 nanorods-graphene composites with 2 V-high voltage and enhanced energy density

Symmetric supercapacitors are often thought to obtain only a narrow voltage range in aqueous electrolytes due to the low thermodynamic electrochemical window of water (1.23 V). Herein, we built a novel symmetric supercapacitor based on Mn3O4@RGO//Mn3O4@RGO (reduced graphene oxide), which maintains a high stable working voltage of 2 V in 1 M Na2SO4 aqueous electrolyte. Increasing the working voltage of the symmetric supercapacitor from 1.0 to 2.0 V can significantly improve the energy storage of the supercapacitor by more than 20 times. Moreover, the symmetric supercapacitor operating at the 2.0 V high voltage can deliver a remarkably high energy density of 42.2 Wh kg−1 at a power density of 500.0 W kg−1 and excellent cycling stability. This work is expected to bring an effective strategy to improve the electrochemical energy storage of metal oxide supercapacitor in aqueous electrolytes.

Enhancement of positive pulsed corona by dielectric enclosure

In this work, the effect of positive pulsed corona enhancement by introducing Teflon dielectric enclosure in vicinity to the electrode assembly was studied. The discharge operating in air without the dielectric was able to operate within a very narrow voltage range of approximately 200 V. The pulsing frequency was below 1.2 kHz and current peaks were below 14 mA. Increasing the applied voltage onto the positive electrode beyond this range would result in sparks between the electrodes. When the Teflon tube enclosure surrounding the high voltage electrode was used, the window of stable pulsed corona operation expanded up to 3-5 kV. The pulsing frequency increased up to 12 kHz and the current peak level increased to approximately 35 mA. Increasing voltage beyond the point with peak pulsing frequency would result in a drop of pulsing frequency until the discharge pulsations stopped completely. The Teflon enclosure was able to enhance the average power deposited into the discharge from 10 to 220 mWatt. In addition, the product gases of the enhanced pulsed corona were tested to be mostly ozone with traceable amount of NO2. The discharge used about 150 eV and 1950 eV per one ozone molecule and nitrogen dioxide molecule respectively. The reported here plasma source is promising from the power density/compactness standpoint since significant enhancement (>20 times) of the energy deposition to the discharge can be achieved compared to that of conventional positive pulsed corona.

Boosting High Energy Density Lithium-Ion Storage via the Rational Design of an FeS-Incorporated Sulfurized Polyacrylonitrile Fiber Hybrid Cathode.

In order to satisfy the escalating energy demands, it is inevitable to improve the energy density of current Li-ion batteries. As the development of high-capacity cathode materials is of paramount significance compared to anode materials, here we have designed for the first time a unique synergistic hybrid cathode material with enhanced specific capacity, incorporating cost-effective iron sulfide (FeS) nanoparticles in a sulfurized polyacrylonitrile (SPAN) nanofiber matrix through a rational in situ synthesis strategy. Previous reports on FeS cathodes are scarce and consist of an amorphous carbon matrix to accommodate the volume changes encountered during the cycling process. However, this inactive buffering matrix eventually increases the weight of the cell, reducing the overall energy density. By the rational design of this hybrid composite cathode, we ensure that the presence of covalently bonded sulfur in SPAN guarantees high sulfur utilization, while effectively buffering the volume changes in FeS. Meanwhile, FeS can compensate for the conductivity issues in the SPAN, thereby realizing a synergistically driven dual-active cathode material improving the overall energy density of the composite. Simultaneous in situ generation of FeS nanoparticles within the SPAN fiber matrix was carried out via electrospinning followed by a one-step heating procedure. The developed hybrid cathode material displays enhanced lithium-ion storage, retaining 688.6 mA h g(FeS@SPANcomposite)-1 at the end of 500 cycles at 1 A g-1 even within a narrow voltage range of 1-3.0 V. A high discharge energy density > 900 W h kg(FeS@SPANcomposite)-1, much higher than the theoretical energy density of the commercial LiCoO2 cathode, was also achieved, revealing the promising prospects of this hybrid cathode material for high energy density applications.

Electroforming and resistive reversible switching effect in polycrystalline fullerene C60 films

It has been found that the conductivity of a polycrystalline fullerene C60 thin film increases by several orders of magnitude after lengthy exposure to an electric field of ∼ 106 V/cm. This effect is called electroforming. After electroforming, the current-voltage characteristic shows high current stability and reproducibility of results. An increase in capacitance and a decrease in resistance by 4 orders is observed in a narrow voltage range of 0.1-1 V, which is the effect of reversible resistive switching. In fields with a strength of 105-106 V/cm, the I-V characteristic of molded films is determined by the current with a limited space charge. Trap concentrations are defined as Nt-1 ≈ 2.3· 1021 m−3 and Nt-2 ≈ 5.8·1020 m−3 and their depth Et ≈ 0.17 eV for polycrystalline C60 films with thicknesses of 250 and 500 nm, respectively.

Resistive switching biodevice composed of MoS2-DNA heterolayer on the gold electrode

Biomolecules have been widely studied for bioelectronic application including biosensors, biomedical devices, biocomputation devices. Among them, the resistive switching biodevices have been developed to demonstrate the resistive switching function based on biomolecules. However, resistive switching biodevices developed so far have some limitations such as narrow voltage range and low stability for practical application. In this study, a heterolayer composed of carboxyl-modified molybdenum disulfide nanoparticles (MoS2) and DNA on the gold (Au) electrode was developed to achieve a wide voltage range and high stability at the nanoscale. To fabricate the resistive switching biodevices, a DNA layer was formed on the electrode through the thiol group on the DNA. The carboxyl-modified MoS2 was then immobilized on the DNA layer (MoS2-DNA heterolayer) through the EDC/NHS reaction. For analyzing the electrical properties, the scanning tunneling spectroscopy investigation showed the resistive switching function of a wide voltage range (4.0 V to −4.0 V) and high stability (10 days) on the MoS2-DNA heterolayer of Au electrodes. The conductivity dramatically increased when the voltage reached 2.4 V, whereas the conductivity abruptly decreased when the voltage reached 0.01 V. From results, we proposed that a MoS2-DNA heterolayer on Au electrode could be utilized as a nanoscale resistive switching layer for the development of nanoscale bioelectronic devices with a wide voltage range and high stability. Based on those advantages, the introduction of MoS2/DNA heterolayer can offer the new direction for development of novel bioelectronic devices.

Novel Alkaline Zn/Na0.44MnO2 Dual-Ion Battery with a High Capacity and Long Cycle Lifespan.

A rechargeable aqueous Zn/Mn battery is a promising device for large-scale energy storage because of its abundant resources, low cost, and high safety. However, its application is plagued by a poor life cycle because of the electrochemical instability of MnO2 in aqueous electrolytes. Here, an alkaline Zn-Na0.44MnO2 dual-ion battery (denoted AZMDIB) is developed for the first time using Na0.44MnO2 as the cathode, a zinc metal sheet as the anode, and a 6 M NaOH aqueous solution as the electrolyte. When the discharge cutoff voltage is lowered to 0.3 V (vs Zn/Zn2+), the Na0.44MnO2 cathode delivers a high capacity of 345.5 mA h g-1 but with a poor cycling performance. The charge-discharge mechanism and structural evolution of the Na0.44MnO2 cathode in an extended potential window (1.95-0.3 V) are also explored. The Na0.44MnO2 electrode experiences two different electrochemical processes: Na+ ions insert/extract reversibly in the potential range of 1.95-1.1 V, and a phase transition occurs from Na0.559MnO2 to Mn(OH)2 below 1.1 V. The latter irreversible reaction is probably due to proton insertion, leading to a severe capacity fade. Nevertheless, in a narrower voltage range (2.0-1.1 V), the AZMDIB full cell exhibits a high reversible capacity (80.2 mA h g-1 at 0.5 C), high rate capability (32 mA h g-1 at 50 C), and excellent cycling stability (73% capacity retention over 1000 cycles at 10 C). Benefiting from the merits of environmental friendliness, cost-effectiveness, and high electrochemical performance, the rechargeable AZMDIB is a promising contender for grid-scale energy storage applications.