Long-term Cycling Tests Research Articles

High-Performance Electrocatalytic Reduction of Nitrite to Ammonia under Ambient Conditions on a FeP@TiO2 Nanoribbon Array.

Electrochemical nitrite (NO2-) reduction is recognized as a promising strategy for synthesizing valuable ammonia (NH3) and degrading NO2- pollutants in wastewater. The six-electron process for the NO2- reduction reaction is complex and necessitates a highly selective and stable electrocatalyst for efficient conversion of NO2- to NH3. Herein, a FeP nanoparticle-decorated TiO2 nanoribbon array on a titanium plate (FeP@TiO2/TP) is proposed as an efficient catalyst for NH3 production under ambient conditions. In 0.1 M NaOH with 0.1 M NO2-, such a FeP@TiO2/TP affords a large NH3 yield of 346.6 μmol h-1 cm-2 and a high Faradaic efficiency of 97.1%. Additionally, it demonstrates excellent stability and durability during long-term cycling tests and electrolysis experiments.

Salt-resistance holocellulose-based solar steam evaporator for desalination brine water

Interfacial solar-powered water evaporation is a cost-effective and sustainable approach using solar energy for seawater desalination. Nevertheless, salt accumulation during solar desalination generally restricts the widespread application of solar vapor generation. Herein, taking merits of the excellent hydrophilicity and inherent porosity of holocellulose (HC), An excellent salt-resistant solar steam evaporator for long-term interfacial solar water desalination was fabricated by decorating polypyrrole (PPy) on the surface of HC. Due to the broadband light absorbance of PPy and the superhydrophilic HC substrate, the PPy-HC evaporator exhibited a high evaporation rate of 1.45 kg m−2 h−1 and conversion efficiency of 93.4 % in a 5 wt% NaCl solution under one sun illumination. Importantly, the evaporator presented superior salt-resistance and stability during long-term cycling test in high salinity brine. This work reveals the key role of superhydrophilicity and water transportation capability in high salt solution solar-driven desalination. Thus, this work provides an effective approach to address the issue of salt accumulation of the traditional evaporator, demonstrating its great potential for real-world solar-driven seawater desalination.

Development of a System for Materials Science Studies on the T-15MD Tokamak

One of the main objectives pursued in carrying out materials science studies on the T-15MD tokamak is to insert samples, including large-scale ones, both for their long-term life cycle tests in the near-wall plasma areas and for studying the effect of impulse loads in the divertor section. A conceptual design of a system for carrying out materials science studies on the T-15MD tokamak has been developed at the Department of General Physics and Nuclear Fusion of the National Research University Moscow Power Engineering Institute. The system will open the possibility to carry out unique experiments on studying the state and composition of the divertor and first wall surfaces without the need to disturb the tokamak chamber vacuum and dismantle the components. It will be possible to perform such studies in the time intervals between tokamak pulses, which will make it possible to reveal changes on the divertor surface after each pulse and estimate correlations between the plasma parameters and changes on the first wall surface. In the attachment assembly, means are provided for cooling the mockups with both water flow and dispersed water-air flow. In addition, various diagnostic devices for monitoring the first wall and divertor surfaces can be installed on the attachment assembly.

Enhancement of La0.8Sr0.2MnO3-based amperometric total NOX sensor via modification with Pt nanoparticles

Pt nanoparticle (PtNP)-modified La0.8Sr0.2MnO3 (LSM)-sensing electrodes (SE) were developed successfully by the impregnation method for amperometric total NOX (NO and NO2) sensors. The structure, morphology, and surface valence state of SE were characterized by thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results showed that all SEs of the sensors were uniformly modified with PtNPs; interestingly, the size of the PtNPs increased with an increase in the modified content. Compared with pure LSM, the sensor based on 0.50 vol% Pt/LSM exhibited enhanced gas-sensing properties toward total NOX. The sensitivity improved from − 9.04 to − 18.7 μA/decade in the NOX, ranging from 50 ppm to 800 ppm. Moreover, the sensor maintained a 94% response signal after a long-term stability test, showing a stable response during the long-term thermal cycling test towards total NOX. Meanwhile, the sensor exhibited markable selectivity and consistency. The catalytic effect of Pt nanoparticles was believed to be the main reason for the enhancement of gas-sensing characteristics.

Comparative Study of Heat-Discharging Kinetics of Fe-Substituted Mn2O3/Mn3O4 Being Subjected to Long-Term Cycling for Thermochemical Energy Storage

The heat-discharging kinetics of an iron-substituted Mn2O3/Mn3O4 redox pair subjected to long-term thermal cycling tests using a temperature swing process at high temperatures was investigated for next-generation concentrated solar power plants equipped with thermochemical energy storage. The heat-discharge mode kinetics for long-term thermal-cycled samples have never been reported. Additionally, comparisons of the heat-discharge mode kinetics for both long-term thermal-cycled and as-prepared samples have never been discussed. In terms of the reproducibility and sustainability of thermochemical energy storage, kinetic evaluations of samples with thermally stable morphologies subjected to long-term thermal cycling at high temperatures are important for next-generation solar thermal power plants. For the long-term thermal-cycled sample, the A2 model based on the Avrami–Erofeev reaction describes the discharging mode behavior in a fractional conversion range of 0–0.24, the contracting area (R2) model best fits in a fractional conversion range of 0.24–0.50, and the third-order (F3) model matches in a fractional conversion range of 0.50–0.70. For the as-prepared sample, the power-law (P2) model describes the behavior of the first part of the discharging mode, whereas the Avrami–Erofeev (A4) model best fits the last half of the discharging mode. The predicted theoretical models for both samples were compared with previous kinetic data.

Defective PrOx for Efficient Electrochemical NO2−-to-NH3 in a Wide Potential Range

Electrocatalytic reduction of nitrite (NO2−) is a sustainable and carbon-neutral approach to producing green ammonia (NH3). We herein report the first work on building defects on PrOx for electrochemical NO2− reduction to NH3, and demonstrate a high NH3 yield of 2870 μg h−1 cm−2 at the optimal potential of –0.7 V with a faradaic efficiency (FE) of 97.6% and excellent FEs of >94% at a wide given potential range (−0.5 to −0.8 V). The kinetic isotope effect (KIE) study suggested that the reaction involved promoted hydrogenation. Theoretical calculations clarified that there was an accelerated rate-determining step of NO2− reduction on PrOx. The results also indicated that PrOx could be durable for long-term electrosynthesis and cycling tests.

Pulsed laser deposited V2O3 thin-films on graphene/aluminum foil for micro-battery applications

The development of new thin-film cathodes triggered a recent research interest in energy storage applications. Over the past years, vanadium oxides have been extensively explored as promising electrodes for batteries owing to their rich valence states and remarkable electrochemical properties. Herein, we report on the synthesis of undoped and Sn doped V2O3 thin-films on graphene (G)/Al foil by pulsed laser deposition followed by rapid thermal annealing in N2 at low temperature (∼430 °C). The obtaining V2O3 phase on graphene/Al foil (G/Al) has been confirmed by X-ray diffraction and Raman and X-ray photoelectron spectroscopy analyses. The synthesized vanadium oxide films were tested as cathodes in coin cells. The electrochemical properties have been systematically investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge discharge (GCD) measurements. A superior electrochemical performance was observed for the V2O3 on G/Al structures, with an initial capacity of around 300 mAh g−1, with respect to the bare G/Al electrode. The use of the Sn-doped (5 mol%) V2O3 thin-films improved slightly the initial capacity up to a value of ca. 311 mAh g−1. Both V2O3/G/Al and Sn-doped V2O3/G/Al exhibited excellent cycling performances after 40 cycles with a capacity maintenance at a C-rate C/20 of 317 mAh g−1. Long-term cycling test (up to 200 cycles) showed that the Sn doping could be an excellent strategy to improve the stability of the electrodes, which yielded a capacity loss of only 0.128% per cycle. Possible mechanisms are presented and discussed. This work could serve as point of reference for future developments in the field of batteries employing vanadium oxide-based thin-films deposited by physical vapor deposition techniques.

Cycle Tests on the Influence of Different Charging Currents—A Case Study on Different Commercial, Cylindrical Lithium Ion Cells

On the way to a Precise Battery, the generation of measurement results and findings based on them play an important role. Although cycle life tests are time-consuming and expensive, they can provide support and important information. Especially in the current topic of accelerating the charging process, it is important to know how different charging currents affect different cell types. The CC CV charging method is still the most common, widely used method. Therefore, long-term cycle tests are carried out in this work in order to clarify the influence of different charging currents, as recommended by the cell manufacturers. Common high-energy and high-power cylindrical lithium ion cells are investigated and compared. In addition to the influence of the charging protocol on the aging, charging time and heating, the effects on the dispersion of the cells as well as the effects on the constant current and the constant voltage part of the charging process are considered. From the results it can be seen how different the investigated cells behave in response to increased charging currents. Even supposedly similar cells show significant differences in aging behavior.

Stable cycling of Si nanowire electrodes in fluorine-free cyano-based ionic liquid electrolytes enabled by vinylene carbonate as SEI-forming additive

Herein, the mixture of the fluorine-free cyano-based ionic liquid N-butyl-N-methylpyrrolidinium tricyanomethanide (Pyr14TCM), lithium dicyanamide (LiDCA) (1:9 salt:IL mole ratio) and 5 wt% vinylene carbonate (VC) is proposed as an electrolyte for the stable electrochemical alloying of silicon nanowire (Si NW) anodes. Detailed electrochemical characterization of the electrolyte (long-term galvanostatic cycling and impedance tests of Si NW-Li half-cells) demonstrates a remarkable cycling performance of the Si anode delivering 1500 mAhg−1 after 500 cycles with 99.5% Coulombic efficiency. The electrode/electrolyte interface is thoroughly investigated via scanning electron microscopy (SEM), energy dispersive X-ray (EDX) mapping, and X-ray photoelectron spectroscopy (XPS). The postmortem analysis reveals the key role of VC in controlling the IL decomposition, resulting in a bilayer solid electrolyte interphase (SEI) formation. The inner layer is mostly composed of graphitic carbon serving as a conductive coating for Si, and inorganic compounds such as Li3N providing high Li-ion conductivity. The outer-layer, is rich in polymeric species ensuring the good mechanical stability and flexibility to withstand the extreme volume change of Si during de-/alloying process, thus explaining the observed prolonged cycling performance.

Strategies for Minimizing Charging Time in Commercial Nickel-Rich/Silicon-Graphite Lithium-Ion Batteries

The emerging nickel-rich/silicon-graphite lithium-ion technology is showing a notable increase in the specific energy, a main requirement for portable devices and electric vehicles. These applications also demand short charging times, while actual charging methods for this technology imply long time or a significant reduction in cycling life. This study analyses the factors that affect the charge behavior for 18,650 commercial nickel-rich/silicon-graphite batteries. For that, long-term cycling tests have been carried out, including electric vehicle standard tests. It can be concluded that this technology has two key issues to develop an efficient charge method: high charge rates should be avoided, mainly below 15% state of charge, and the charge should be finished at 95% of actual cell capacity. This allows that, regardless of application and cell degradation level, cells can be recharged in 2 h without a negative impact on cycling life. For faster charge applications, a new method has been developed to minimize charging time without compromising the cycle life as much as the high current manufacturer method. The proposed fast charge method has proven to be notably faster, recharging in an average 1.3 h (48% less than the high current method and 68% less than the standard method).

Structure and electrochromic properties of WO3 thin films by direct current, pulsed direct current, and radio frequency magnetron sputtering from metallic and ceramic targets

The structure, morphology, and electrochromic properties of sputtered-WO3 thin films from ceramic and metallic targets were investigated. The films were produced using different types of power sources, namely, direct current (DC), pulsed DC, and radio frequency (RF) generators. Highly transparent as-deposited WO3 thin films grown at room temperature using each target changed to dark blue upon introduction of an electric field in electrolyte regardless of types of sputtering power. WO3 films obtained by sputtering the ceramic target using a pulsed DC power exhibited a large transmittance difference of 97.5% and high coloration efficiency of 55.2 cm2/C compared to the films using DC and RF powers, these films had higher response speeds and stable transmittance modulation after long-term cycle tests. WO3 thin films produced by sputtering a metallic tungsten target showed enhanced electrochromic performance when grown under DC power and a coloration efficiency of 69.1 cm2/C due to their porous microstructure. This article presents methods for the fabrication of low-cost and large-scale oxide electronic devices for various applications, such as electrochromic displays, that can be applied for mass production.

Lithium Difluoro(dioxalato) Phosphate as an Electrolyte Additive for NMC811/Graphite Li-ion Pouch Cells

Lithium difluoro(dioxalato)phosphate (LiDFDOP) has been systemically studied as an electrolyte additive singly and in combination with co-additives fluoroethylene carbonate (FEC) and vinylene carbonate (VC) in LiNi0.8Mn0.1Co0.1O2 (NMC811)/artificial graphite (AG) pouch cells. Long-term cycling tests at room and elevated temperatures (20 °C, 40 °C, and 55 °C) with different upper cutoff voltages (4.06 V and 4.20 V) were performed. These results were combined with ultra-high precision coulometry (UHPC), ex-situ gas measurements, and automatic cell storage tests to reveal multiple aspects of cell performance. A density functional theory (DFT) calculation has also been performed and compared to formation data to reveal the mechanistic aspects of LiDFDOP reduction. Radar plots and a figure-of-merit (FOM) approach were further utilized to summarize results and rank additive and additive combination performance for the NMC811/AG cells. This work highlights an effective additive and suitable co-additives for use in NMC811/graphite cells and gives important insights for future electrolyte additive studies.

N-doped porous carbon from direct KOH activation of Victorian brown coal for high-rate energy storage performance

N-doped highly porous carbons (NHPCs) derived from Victorian brown coal (VBC) were prepared through direct KOH activation in the presence of urea as the N source. Different weight ratios of KOH (VBC-urea mixture: KOH=1:0, 1:1, 1:2, and 1:3) have been used to optimize the porosity of NHPCs. Benefiting from the synergistic effect of the high porosity and N doping, the synthesized material with a high specific surface area of 687 m2/g and the N content at ∼11 at% exhibited a high specific discharge capacity of 604.6 mAh/g at a current density of 0.1 A/g after 100 cycles and a high-rate performance of 245 mAh/g at 3 A/g. The developed material delivered a reversible capacity of 707.7 mAh/g at 0.05 A/g at the end of rate performance. The long-term cycling test performed at 1 A/g illustrates a stable and reversible capacity of 268 mAh/g after 1000 cycles with a coulombic efficiency of 100% and charge retention of 88%. The hierarchically porous carbon matrix with N doping can increase the Li+ diffusion efficiency and accelerate the charge transfer, thus leading to enhanced high-rate performance, superior reversibility, and high cyclic stability.

Electrolyte Development for Fast Charging of High Energy Density Li-Ion Cells

Different lithium salt concentrations in carbonate electrolyte were studied on the fast charging performance of LiNi0.6Mn0.2Co0.2O2 (NMC622)/graphite pouch cells. The cells with electrolyte concentration from 0.75 M to 1.50 M showed similar fast charging capabilities. Further increase of the concentration to 1.75 M and 2.00 M decreased the attainable capacity in fast charging. In the long-term cycling test, the capacity retention after 200 fast charging cycles increased with the increase of salt concentration in electrolyte. Cells with 1.5 M electrolyte showed the best overall performance in fast charging capacity and long-term cycling. Li plating were observed in the cells with 0.75 M, 1.00 M and 1.25 M electrolyte. It was improved with greatly reduced Li plating area in 1.50 M, and no Li plating at all in 1.75 M and 2.00 M electrolyte. Post-mortem analysis such as neutron powder diffraction (NPD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the electrode after cycling. It suggests that electrolyte concentration needs to be optimized for a given cell configuration with specific electrode and loading. Figure 1

High-Performance Ni-Rich Cathodes through Precision Control for Electric Vehicle Batteries

Li-ion batteries (LIBs) become the main portable energy source for electric vehicles (EVs) owing to their high energy and power densities as compared to those of other forms of secondary batteries. As the overall performance and cost of LIBs are largely determined by the cathode material, recent research has heavily focused on developing high-capacity cathode materials. However, chasing high-energy-density without compromising service life is very challenging. Among the available cathode materials for LIBs, layered Li[Ni1-x-yCox(Mn or Al)y]O2 (NCM or NCA) is the material of choice owing to its high theoretical capacity of 275 mAh g−1. The demand for higher energy density at a lower cost has pushed the Ni content to approach 90% because Ni is in charge of energy density in NCM and NCA cathode. The inclusion of more Ni in the NCM and NCA cathodes has significant benefits in LIB energy density and cost, as it concomitantly reduces the content of expensive Co. However, the increase in Ni content sacrifices cycling and thermal stability due to the high reactivity of Ni. Such a trade-off between energy density and stability becomes increasingly severe with increasing Ni content. Capacity fading of Ni-rich NCM and NCA cathodes, especially above Ni 80%, largely originates from microcracking which exposes a large portion of the cathode interior to deleterious electrolyte attack. To suppress the development of microcracks on cathode materials, Ni-rich cathode materials should guarantee mechanical stability even in highly charged states. In this presentation, Ni-rich layered cathodes through precision control are presented. One approach is an optimization of both the crystal structure and primary particle morphology by introducing high valence ions. Another strategy is to develop concentration gradient (CG) cathodes with rod-shaped primary particles that are elongated along the radial direction. The CG cathodes are further optimized via high-valence ion doping thereby preserving the microstructure until the cathode attains optimal crystal structure via the reduction of cation mixing. These cathodes exhibit outstanding performance in long-term cycling tests.

Reconstructing proton channels via Zr-MOFs realizes highly ion-selective and proton-conductive SPEEK-based hybrid membrane for vanadium flow battery

There is an urgent need to break through the trade-off between proton conductivity and ion selectivity of proton exchange membrane (PEM) in vanadium flow battery (VFB). Proton channels in PEM are the key to controlling the ion sieving and proton conductivity in VFB. Herein, two types of proton channels are reconstructed in the hybrid membrane via introducing modified Zr-MOFs (IM-UIO-66-AS) into SPEEK matrix. Internal proton channels in IM-UIO-66-AS and interfacial proton channels between grafted imidazole groups on Zr-MOFs and SPEEK greatly improve the conductivity of the IM-UIO-66-AS/SPEEK hybrid membrane. More importantly, both reconstructed proton channels block the vanadium-ion permeation to realize enhanced ion selectivity according to the size sieving and Donnan exclusion effects, respectively. Moreover, the hybrid membrane exhibits good mechanical property and dimensional stability. Benefiting from such rational design, a VFB loading with the optimized membrane exhibits enhanced voltage efficiency of 79.9% and outstanding energy efficiency of 79.6% at 200 mA cm−2, and keeps a notable cycle stability for 300 cycles in the long-term cycling test. Therefore, this study provides inspiration for preparing next-generation PEMs with high ion selectivity and proton conductivity for VFB application.

Understanding the effect of salt concentrations on fast charging performance of Li-ion cells

Different lithium salt (lithium bis(fluorosulfonyl) imide (LiFSI)/LiPF6 9/1 mol ratio) concentrations in carbonate electrolyte were studied on the fast charging performance of LiNi0.6Mn0.2Co0.2O2 (NMC622)/graphite pouch cells. The cells with electrolyte concentration from 0.75 M to 1.50 M showed similar fast charging capabilities. Further increase of the concentration to 1.75 M and 2.00 M decreased the attainable capacity in fast charging. In the long-term cycling test, the capacity retention after 200 fast charging cycles increased with the increase of salt concentration in electrolyte. Cells with 1.5 M electrolyte showed the best overall performance in fast charging capacity and long-term cycling. Li platings were observed in the cells with 0.75 M, 1.00 M and 1.25 M electrolyte. It was improved with greatly reduced Li plating area in 1.50 M, and no Li plating at all in 1.75 M and 2.00 M electrolyte. Post-mortem analysis such as neutron powder diffraction (NPD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the electrode after cycling. It suggests that electrolyte concentration needs to be optimized for a given cell configuration with specific electrode and loading.

Long-Term Thermal Cycling Test and Heat-Charging Kinetics of Fe-Substituted Mn2O3 for Next-Generation Concentrated Solar Power Using Thermochemical Energy Storage at High Temperatures

We studied the performance in terms of the long-term cyclic thermal storage and heat-charging kinetics of Fe-substituted manganese oxide for use in thermochemical energy storage at temperatures exceeding 550 °C in a next-generation concentrated solar power system in which a gas stream containing oxygen is used for reversible thermochemical processes. The Fe-substituted Mn2O3 was evaluated from the viewpoint of its microstructural characteristics, thermodynamic phase transitions, and long-term cycling stability. A kinetic analysis of the heat-charging mode was performed at different heating rates to formulate the kinetic equation and describe the reaction mechanism by determining the appropriate reaction model. Finally, the kinetics data for the sample obtained after the long-term cycling test were compared and evaluated with those of the as-prepared sample and kinetic literature data tested under different conditions. For the long-term cycled sample, the Avrami–Erofeev reaction model (An) with n = 2 describes the behavior of the first part of the charging mode, whereas the contracting area (R2) reaction model best fits the last half of the charging mode. For the as-prepared sample, except for the early stage of the charging mode (fractional conversion < 0.2), the contracting volume (R3) reaction model fits the charging mode over a fractional conversion range of 0.2–1.0 and the first-order (F1) reaction model fits in the fractional conversion range of 0.4–1.0. The predicted kinetic equations for both the samples were in good agreement with the experimental kinetic data.

Charge–Discharge Behavior of Graphite Negative Electrodes in FSA-Based Ionic Liquid Electrolytes: Comparative Study of Li-, Na-, K-Ion Systems

K-ion batteries utilizing ionic liquid (IL) electrolytes are promising candidates for next-generation batteries because of the abundance of potassium resources, low redox potential of potassium, and high safety of ILs. Our major interest is in the comprehensive understanding of electrochemical alkali metal intercalation/deintercalation into graphite negative electrodes, because graphite can easily form graphite intercalation compounds (GICs) with various ionic species, but not with sodium. In this study, we investigated the potassium storage mechanism of graphite negative electrodes in bis(fluorosulfonyl)amide (FSA)-based ILs, and compared the electrochemical GIC formation of Li-, Na-, and K-ion systems. Charge–discharge tests of graphite in K[FSA]–[C3C1pyrr][FSA] IL (C3C1pyrr = N-methyl-N-propylpyrrolidinium) at 313 K yielded an initial discharge capacity as high as 268 mAh (g-C)−1, leading to the formation of several K-GICs including stage-3 KC36, stage-2 KC24, and stage-1 KC8. The rate capability and long-term cycling tests indicated stable potassiation/depotassiation behavior for 225 cycles. A comparison of the electrochemical behavior of graphite among M[FSA]–[C3C1pyrr][FSA] (M = Li, Na, and K) ILs at 298 K indicated that the formation of binary M-GICs is localized in the potential range below −2.85 V vs. Fc+/Fc (Fc = ferrocene), which possibly hinders Na-GIC formation.

The construction of carbon nanofiber composites modified by graphene/polypyrrole for flexible supercapacitors

Carbon nanofibers (CNFs) have attracted considerable attention because they make it possible for materials to have a variety of enhanced properities. However, the unsatisfied electrochemical performance of an individual component and the poor electrical conductivity caused by insufficient physical contact points become the fully addressing issues when CNFs are proposed as electrode material in a flexible supercapacitor. Hence, this paper proposes a feasible perspective on enhancing the electrochemical performance and flexibility via the method of electrostatic self-assembly and the “dipping and drying” strategy. The reduced graphene oxide (rGO) layer is uniformly anchored on the surface of SnCl2 modified carbon-based fiber polyacrylonitrile (PAN) fabricated by the electrospinning method. Pseudocapacitance material polypyrrole (PPy) is subsequently deposited and selected to design a composite PAN@rGO@PPy electrode. As expected, the as-constructed binder-free PAN@rGO@PPy electrode shows a specific capacitance of 203 F g−1; the assembled flexible supercapacitor delivers a high energy density of 15 Wh kg−1 together with a power density of 500 W kg−1, and displays remarkable cycling stability after 10,000 cycles. Finally, the flexibility via various deformations is discussed, meanwhile, the structural and compositional stability of the PAN@rGO@PPy electrode during long-term cycling test are demonstrated. In light of the facile preparation strategy and the excellent electrochemical performance, this work offers an instructive direction for the development of flexible energy storage devices.