Extended Voltage Range Research Articles

Low mass loading of graphene quantum dots on titanium nitride nanotube arrays for boosting capacity and operating voltage of symmetric supercapacitor in an aqueous electrolyte

Compared to other supercapacitors, aqueous supercapacitors offer reliability, a long lifecycle, and affordability. However, the significant challenge in advancing aqueous supercapacitors lies in their limited operating voltage window. This limitation has resulted in a notable reduction in energy density. Therefore, contemporary electrode materials exhibiting high electrochemical activity and wide operating potential windows are imperative. This study introduces a technique that not only boosts energy density but also signifies a significant breakthrough for metal nitride-based aqueous supercapacitors. This method broadens the operating voltage range and necessitates optimization of the heterostructure design. A distinctive titanium nitride/graphene quantum dot (TiN/GQD) heterostructure was synthesized through electrophoretic deposition of GQDs onto plasma-nitrided TiO2 nanotubes. This novel heterostructure demonstrates the capability to function across an extended voltage range of 2 V. It is noteworthy that the TiN/GQD nanocomposite has excellent bonding at the interface of TiOC and a large surface area, resulting in an exceptional areal capacitance of 190 mF cm−2 at a current density of 0.2 mA cm−2 in 0.5 M Na2SO4 aqueous solution. It also displays excellent cycle stability (91.5 % after 6000 galvanostatic charge-discharge cycles). Moreover, the optimum GQDs deposition time (15 min) was determined to achieve the most efficient electrochemical performance. Furthermore, a symmetric TiN/GQD-15 supercapacitor device was assembled, reaching a high energy density of 8.2 Wh kg−1 at a power density of 77 W kg−1.

An aqueous electrolyte densified by perovskite SrTiO3 enabling high-voltage zinc-ion batteries

The conventional weak acidic electrolyte for aqueous zinc-ion batteries breeds many challenges, such as undesirable side reactions, and inhomogeneous zinc dendrite growth, leading to low Coulombic efficiency, low specific capacity, and poor cycle stability. Here, an aqueous densified electrolyte, namely, a conventional aqueous electrolyte with addition of perovskite SrTiO3 powder, is developed to achieve high-performance aqueous zinc-ion batteries. The densified electrolyte demonstrates unique properties of reducing water molecule activity, improving Zn2+ transference number, and inducing homogeneous and preferential deposition of Zn (002). As a result, the densified electrolyte exhibits an ultra-long cycle stability over 1000 cycles in Zn/Ti half cells. In addition, the densified electrolyte enables Zn/MnO2 cells with a high specific capacity of 328.2 mAh g−1 at 1 A g−1 after 500 cycles under an extended voltage range. This work provides a simple strategy to induce dendrite-free deposition characteristics and high performance in high-voltage aqueous zinc-ion batteries.

Dynamic Structure Evolution of Extensively Delithiated High Voltage Spinel Li1+xNi0.5Mn1.5O4 x < 1.5.

High voltage spinel is one of the most promising next-generation cobalt-free cathode materials for lithium ion battery applications. Besides the typically utilized compositional range of LixNi0.5Mn1.5O4 0 < x < 1 in the voltage window of 4.90-3.00 V, additional 1.5 mol of Li per formula unit can be introduced into the structure, in an extended voltage range to 1.50 V. Theoretically, this leads to significant increase of the specific energy from 690 to 1190 Wh/kg. However, utilization of the extended potential window leads to rapid capacity fading and voltage polarization that lack a comprehensive explanation. In this work, we conducted potentiostatic entropymetry, operando XRD and neutron diffraction on the ordered stoichiometric spinel LixNi0.5Mn1.5O4 within 0 < x < 2.5 in order to understand the dynamic structure evolution and correlate it with the voltage profile. During the two-phase reaction from cubic (x < 1) to tetragonal (x > 1) phase at ∼2.8 V, we identified the evolution of a second tetragonal phase with x > 2. The structural evaluation during the delithiation indicates the formation of an intermediate phase with cubic symmetry at a lithium content of x = 1.5. Evaluation of neutron diffraction data, with maximum entropy method, of the highly lithiated phase LixNi0.5Mn1.5O4 with 2 < x < 2.5 strongly suggests that lithium ions are located on octahedral 8a and tetrahedral 4a positions of the distorted tetragonal phase I41amd. Consequently, we were able to provide a conclusive explanation for the additional voltage step at 2.10 V, the sloping voltage profile below 1.80 V, and the additional voltage step at ∼3.80 V.

Stability of Power Supply Bootstrapped Unity-Gain Buffers

Power-supply bootstrapping is a technique based on applying a DC-shifted copy of the input signal to the supply terminals of an operational amplifier (OA). It is usually applied configuring the OA as a unity-gain buffer, and achieves an increased input impedance or an extended voltage range for a device. However, bootstrapped circuits can become unstable for reasons that are not evident when considering the most simple OA models. In this brief, we show the mechanism producing instabilities in these circuits and the necessary equations for stability analysis are determined. Stability can be studied by considering the power-supply and common-mode rejection ratio curves thanks to an intrinsic relationship between them. A realistic OA model from the literature was chosen as validation for the presented method and as a study-case to show the rationale for the stability analysis and possible compensation strategies. The proposed method was successfully applied to compensate bootstrapped buffers in experimental tests.

Effect of Cu substitution on anion redox behaviour in P3-type sodium manganese oxides

Sodium layered oxides which display oxygen anion redox behaviour are considered promising positive electrodes for sodium-ion batteries because they offer increased specific capacities. However, they suffer from irreversible structural changes resulting in significant capacity loss and limited oxygen redox reversibility. Here the effect of Cu substitution on the electrochemical performance of P3-type sodium manganese oxide is examined by evaluating the structural and electronic structural evolution upon cycling, supported by density functional theory (DFT) calculations. Over the voltage range 1.8–3.8 V vs. Na/Na+, where the redox reactions of the transition metal ions contribute entirely towards the charge compensation mechanism, stable cycling performance is maintained, showing a capacity retention of 90% of the initial discharge capacity of 166 mA h g−1 after 40 cycles at 10 mA g−1. Over an extended voltage range of 1.8–4.3 V vs. Na/Na+, oxygen anion redox is invoked, with a voltage hysteresis of 110 mV and a greater initial discharge capacity of 195 mA h g−1 at 10 mA g−1 is reached. Ex-situ powder x-ray diffraction patterns reveal distortion of the P3 structure to P′3 after charge to 4.3 V, and then transformation to O′3 upon discharge to 1.8 V, which contributes towards the capacity fade observed between the voltage range 1.8–4.3 V. DFT with projected density of states calculations reveal a strong covalency between the copper and oxygen atoms which facilitate both the cationic and anionic redox reactions in P3-type Na0.67Mn0.9Cu0.1O2.

Water-in-Salt Electrolyte-Based Extended Voltage Range, Safe, and Long-Cycle-Life Aqueous Calcium-Ion Cells.

The narrow electrochemical stability window (1.23 V) of an aqueous electrolyte hinders the practical realization of calcium-ion chemistries of high-energy-density and long-cycle-life batteries. Furthermore, developing an aqueous electrolyte that is low cost, is environmentally friendly, and has a wide voltage window is essential to designing safe, high-energy-density, and sustainable calcium-ion batteries. A calcium-based water-in-salt (WISE) aqueous electrolyte surpasses the narrow stability window by offering a 2.12 V wide window by suppressing the hydrogen evolution at the anode and minimizing the overall water activity at the cathode. A comprehensive theoretical study predicts the preferential reduction of salt aggregates over water to form a passivation layer at the electrode-electrolyte interface and enhance the electrolyte stability window. Additionally, Raman spectroscopy reveals that the calcium ion coordination number, which is the number of nitrate ions surrounding the calcium ions in the aqueous electrolyte, gradually increases with an increase in the electrolyte concentration, leading to a gradual decrease in the hydration number of the calcium ions. A full cell in WISE was demonstrated to exhibit an excellent rate capability and cycling stability with negligible capacity loss (0.01 per cycle), maintaining 80% capacity retention over 1800 cycles with ∼99.99% Coulombic efficiency. The full cell provides an energy density of 232 Wh kg-1 at a power density of 69 W kg-1 and a current rate of 0.15 A g-1. Even at a higher current rate of 5 A g-1, the battery delivers an energy density of 182 Wh kg-1 (based on the active mass of the anode). This is one of the best performances to date of all previously reported full-cell aqueous calcium-ion batteries. A fundamental understanding of the storage mechanism and a electrode degradation study was achieved. This work suggests and expands new avenues for the practical realization of low-cost, safe, eco-friendly, and high-performance aqueous calcium-ion batteries for future large storage applications.

Reverse-Bias and Temperature Behaviors of Perovskite Solar Cells at Extended Voltage Range.

Perovskite solar cells have reached certified power conversion efficiency over 25%, enabling the realization of efficient large-area modules and even solar farms. It is therefore essential to deal with technical aspects, including the reverse-bias operation and hot-spot effects, which are crucial for the practical implementation of any photovoltaic technology. Here, we analyze the reverse bias (from 2.5 to 30 V) and temperature behavior of mesoscopic cells through infrared thermal imaging coupled with current density measurements. We show that the occurrence of local heating (hot-spots) and arc faults, caused by local shunts, must be considered during cell and module designing.

β-LiVP2O7 as a positive electrode material for Li-ion batteries

A novel polymorph of lithium vanadium pyrophosphate has been obtained using electrochemical Na+ for Li+ exchange in β-NaVP2O7. β-LiVP2O7 has a triclinic KAlP2O7-type structure with large tunnels along the [100] direction and demonstrates electrochemical capacity of 100 mAh g−1 within a high-voltage region of 4.0-4.2 V vs. Li/Li+ with excellent C-rate capability: increasing discharge current density from C/10 to 10C results in a capacity drop of only 7%. The (de)intercalation process is characterized by a solid solution-like behavior with the diffusion coefficient amounting to 10−12 – 10−11 cm2 s−1. A redox process at ~ 1.8 V vs. Li/Li+ leads to 200 mAh g−1 of the overall intercalation capacity within the extended voltage range that corresponds to “β-VP2O7 ↔ β-Li2VP2O7” two-electron process.

Switched-Capacitor Boost-Buck Ladder Converters With Extended Voltage Range in Standard CMOS

This paper presents fully integrated switched-capacitor boost-buck power converters with conversion ratios 5, 7, and 1/5. Such converters operate over a voltage range extended beyond the device ratings due to a low-voltage-stress configuration, accumulation-mode NMOS capacitors, and a circuit technique for switch bootstrapping. After modeling the simple and the symmetrical ladder converters, we determined methods for assessing the device working voltages and for optimizing the sizes of capacitors and switches. The key performance parameters were compared and the losses due to non-linear parasitic capacitances were calculated. The characterization of the prototypes in a 1.8-3.3-V, 0.18-$\mu \text{m}$ CMOS process demonstrated a 15 V range, a 5.4 mW/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> output power density, and good correlation between measured and predicted results.

In situ spectroelectrochemical ellipsometry using super continuum white laser: Study of the anodization of magnesium alloy

This work shows the interest to use a real time, white laser-based ellipsometer to characterize a complex electrolyte|electrode interface during an electrochemical process in an aqueous-based medium. This method is proposed to probe electrochemical interfaces that are usually not suitable to the full extent application of ellipsometry due to great disturbance of the reflected light flux provoked by gas evolution or roughness. In situ spectroelectrochemical ellipsometry combining such a visible super continuum fiber laser-band source was not previously reported to the best of the authors’ knowledge. The setup was employed to monitor an electrochemical process whose mechanism was previously incompletely described: the prespark anodization regime of the plasma electrolytic oxidation process of the Mg alloy AZ91D in the 3M KOH electrolyte. Above the anodization voltage of 4 V, the side water oxidation reaction induced light diffusion that reduces reflected light beam intensity. The process is monitored in an extended voltage range from 4 to 40 V and in an extended spectral range (495–800 nm). In the presented case, the use of a visible super continuum fiber laser-band source enhanced the signal-to-noise ratio giving access to a deeper picture of the triplex layer structure during surface repassivation by monitoring the evolution of the outer, inner, and interfacial layers.

Formation of needle-like porous CoNi2S4-MnOOH for high performance hybrid supercapacitors with high energy density

Seeking for suitable electrode materials and designing rational porous structures are great challenges for developing high performance supercapacitors. Herein, needle-like porous CoNi2S4-MnOOH (denoted as NCS-MO) were prepared via a simple two steps solvothermal method and used as battery-type electrode of supercapacitor for the first time. Owing to the multiple oxidation states of needle-like porous NCS-MO and the inherent porous structure, the electrode delivers outstanding electrochemical capacitive properties with a high gravimetric specific capacitance of 1267.7 F g−1 at the scan rate of 1 mV s−1. To further assess the practical electrochemical performances, we assembled a hybrid supercapacitor using the as-synthesized porous NCS-MO as cathode and active carbon as anode. The device exhibits excellent performance with a high energy density of 47.1 Wh kg−1 at the power density of 998 W kg−1 in an extended voltage range of 1.6 V and outstanding cycling stability. These results demonstrate that the needle-like porous NCS-MO could be promising potential electrode material for high performance supercapacitor.

Enhanced capacitive properties of all-metal-oxide-nanoparticle-based asymmetric supercapacitors.

The major problem of transition metal oxide (TMO)-based supercapacitors is their low specific energy (Esp) due to the poor electrical conductivity of the TMO electrodes and narrow operating voltage window. To solve these limitations simultaneously, we propose asymmetric supercapacitors (ASCs) consisting of two composite TMO electrodes working in different potential ranges. Titanium dioxide (TiO2) nanoparticle (NP)-incorporated iron oxide (Fe2O3) and manganese oxide (MnO2) NPs were used as electrode materials covering the negative and positive potential window, respectively. The specific capacitance (Csp) of this asymmetric TiO2–Fe2O3‖TiO2–MnO2 supercapacitor is comparable to that of the symmetric TiO2–MnO2‖TiO2–MnO2 supercapacitor. However, the ASC can operate over a doubly extended voltage range, which resulted in a significant enhancement in the specific energy of the device. The Esp value of the ASC at a specific power of 1000 W kg−1 is 48.6 W h kg−1, which is 34.1 and 8.1 times, respectively, larger than that of the two symmetric devices.

Characterization of cadmium sulfide buffer layers using electrolyte contacts

Electrolyte contacts were used to characterize cadmium sulfide (CdS) films grown by chemical bath deposition on fluorine-doped tin oxide glass (FTO). Capacitance measurements were made in a buffered electrolyte free of redox species, and cyclic sweep voltammetry was carried out using an electrolyte containing Fe(CN)64− ions. A theoretical model was developed to describe the influence of pinholes on Mott Schottky plots of CdS-coated FTO. The model allows estimation of the pinhole coverage by fitting the Mott Schottky plot over an extended voltage range. Cyclic voltammetry in a hexacyanoferrate(II) electrolyte also allows detection of pinholes, but quantitative estimation of pinhole coverage is complicated by the fact that diffusion of Fe(CN)64− to pinholes occurs by hemispherical diffusion, which can substantially enhance the current response. Comparison of the results of capacitance and voltammetry measurements provides insights into average pore size and number density. Results presented for CdS films grown using two different chemical bath compositions reveal substantial differences in pinhole numbers and doping density.

Electrochemical performance of ZnO-coated Li4Ti5O12 composite electrodes for lithium-ion batteries with the voltage ranging from 3 to 0.01 V.

Oxide is widely used in modifying cathode and anode materials for lithium-ion batteries. In this work, a facile method of radio magnetron sputtering is introduced to deposit a thin film on Li4Ti5O12 composite electrodes. The pristine and modified Li4Ti5O12 electrodes are characterized at an extended voltage range of 3–0.01 V. The reversible capacity reaches a high level of 286 mAh g−1, which is a little less than its theoretical capacity (293 mAh g−1). Electrodes modified by ZnO thin films with various thickness show elevated rate capability and improved cycle performance.

Li-rich and Ni-rich transition metal oxides: Coating and core-shell structures

In this work, we consider influence of synthesis procedures, applying coatings, and formation of core-shell structures on the electrochemical performance of Ni-rich and Li-rich oxides. Li-rich Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials synthesized by different synthesis procedures exhibit different electrochemical behavior, especially those obtained by sol-gel combustion method. The TEM findings reveal the presence of monoclinic and trigonal phases in the Li-rich materials synthesized. TEM/ED/EDX microanalysis shows that the C2/m monoclinic phase appears to have a variable composition Li2[M]O3, where [M] = (Mn, Ni, Co). Whence, on the basis of monoclinic phase we can observe a restricted solid solution with 4 h-Wyckoff Mn-cation positions potentially being occupied by the mixture of three 3d-metal cations [M] = (Mn, Ni, Co). The cyclability of Li-rich oxides is improved by thin alumina films deposited by ALD directly on porous electrodes. The better capacity retention of modified electrodes is explained by suppressing reactions with electrolyte accompanied by growth of SEI film on cathode. The core-shell structures with Ni-rich core and gradient shell enriched with Mn were obtained by coprecipitation and applying the shell material onto LiNi0.8Co0.15Al0.05O2 as received. These structures show better cyclability and rate capability in the extended voltage range of 2.5–4.4 V than the core materials.

Voltage dependent STM imaging of inorganic adsorbates

Scanning tunneling microscopy is sensitive to surface adsorbates to a much lower impurity level than most other surface science techniques. Even under the best vacuum and preparation conditions, a very low concentration of depressions of unknown origin is often observed in STM images of the coin metal surfaces. We outline a procedure to identify impurities by apparent height spectroscopy; a technique that can be easily performed by standard scanning tunneling microscopes. Apparent height spectroscopy, performed with a low-temperature scanning tunneling microscope, records the apparent height of an adsorbate with respect to the surface level over an extended voltage range at distinct voltage intervals. The spectra show characteristic features that can be used to identify adsorbates. We exemplify our method for two common impurities on Cu(111), oxygen atoms and carbon monoxide molecules. We reveal three characteristic differences in the apparent height spectroscopy of the two adsorbates: the dark region, the voltage of contrast reversal, and the onset of the lowest unoccupied molecular orbital. Each of these features is characteristic for the specific adsorbate/substrate system; giving three possibilities to identify the two species. The procedure can easily be extended to other impurities.

Self-assembled Li3V2(PO4)3/reduced graphene oxide multilayer composite prepared by sequential adsorption

Herein, we report on Li3V2(PO4)3 (LVP)/reduced graphene oxide (rGO) multilayer composites prepared via a sequential adsorption method and subsequent heat treatment, and their use as cathodes for high-rate lithium-ion batteries. The sequential adsorption process includes adsorbing oppositely charged components of anionic inorganic species and cationic head of a surfactant adsorbed to graphite oxide sheets, which is a key step in the fabrication of the LVP/rGO multilayer composites. The multilayer structure has open channels between the highly conductive rGO layers while achieving a relatively high tap density, which could effectively improve the rate capability. Consequently, the LVP/rGO multilayer composites exhibit a high tap density (0.6 g cm−3) and good electrochemical properties. Specifically, in the voltage range of 3.0–4.3 V, the composite exhibits a specific capacity of 131 mAh g−1 at 0.1C, a good rate capabilities (88% capacity retention at 60C), and long cycling performance (97% capacity retention after 500 cycles at 10C). Moreover, in the extended voltage range of 3.0–4.8 V, it exhibits a high specific capacity of 185 mAh g−1 at 0.2C, a good rate capability (66% capacity retention at 30C), and stable cycling performance (96% capacity retention after 500 cycles at 10C).

Dual-bridge LLC-SRC with extended voltage range for deeply depleted PEV battery charging

ABSTRACTThis paper proposes a dual-bridge LLC series resonant converter with hybrid-rectifier for achieving extended charging voltage range of 50–420 V for on-board battery charger of plug-in electric vehicle for normal and deeply depleted battery charging. Depending upon the configuration of primary switching network and secondary rectifier, the proposed topology has three operating modes as half-bridge with bridge rectifier (HBBR), full-bridge with bridge rectifier (FBBR) and full-bridge with voltage doubler (FBVD). HBBR, FBBR and FBVD operating modes of converter achieve 50–125, 125–250 and 250–420 V voltage ranges, respectively. For voltage above 62 V, the converter operates below resonance frequency zero voltage switching region with narrow switching frequency range for soft commutation of secondary diodes and low turn-off current of MOSFETs to reduce switching losses. The proposed converter is simulated using MATLAB Simulink and a 1.5 kW laboratory prototype is also built to validate the operation of proposed topology. Simulation and experimental results show that the converter meets all the charging requirements for deeply depleted to fully charged battery using constant current-constant voltage charging method with fixed 400 V DC input and achieves 96.22% peak efficiency.

Rejuvenation of degraded electrochromic MoO3 thin films made by DC magnetron sputtering: Preliminary results

Molybdenum oxide thin films were deposited by reactive DC magnetron sputtering and were subjected to voltammetric cycling in an electrolyte comprised of lithium perchlorate in propylene carbonate. The films were heavily degraded during 20 voltammetric cycles in an extended voltage range. The films were subsequently rejuvenated by use of potentiostatic treatments under different voltages during 20 hours. Optical changes were recorded during the electrochemical degradation and ensuing rejuvenation.

Tailorable electrochemical performance of spinel cathode materials via in-situ integrating a layered Li2MnO3 phase for lithium-ion batteries

Abstract Electrochemical performances of spinel cathode materials have been evaluated in a broad voltage range of 2.0–4.8 V vs. Li/Li+ via in-situ integrating a layered Li2MnO3 phase for high-voltage and high-capacity lithium ion batteries. Effects of sintering temperatures on manipulating hybrid spinel-layered structures have been systematically studied during the decomposition of nonstoichiometric Li0.65Mn0.59Ni0.12Co0.13Oδ material. The spinel component undergoes a phase transition from an initial Li4Mn5O12-type to a LiMn1.5Ni0.5O4-type spinel structure under high temperatures above 700 °C; meanwhile the content of layered Li2MnO3 component is increased. Li2MnO3-stabilized spinel-layered cathodes can deliver the discharge capacity more than 225 mA h/g at 0.1 C and exhibit outstanding capacity retentions above 90% at 0.5 C (1 C = 250 mA/g) in an extended voltage range between 2.0 and 4.8 V. In addition to clarify significant Li2MnO3 impacts on improving cycling stability of spinel cathode materials, it is noticeable that LiMn1.5Ni0.5O4-based spinel materials can effectively suppress the electrochemical activation of the layered Li2MnO3 up to 4.8 V. This work sheds lights on tailoring hybrid structures and maximizing electrochemical performances of Li2MnO3-based spinel-layered cathode materials for superior lithium ion batteries.