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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Insights into the Enhanced Reversibility of Graphite Anode Upon Fast Charging Through Li Reservoir

Increasing the charging rate and reducing the charging time for Li-ion batteries are crucial to realize the mainstream of electric vehicles. However, it is formidable to avoid the Li plating on graphite anode upon fast charging. Despite the tremendous progress in Li detection techniques, the fundamental mechanism of Li plating and its chemical/electrochemical responses upon cycling still remains elusive. Herein, we present a comprehensive electrochemical method to investigate the fast charging behavior of graphite electrode. A detailed analysis is directed toward understanding the changes in phase, composition, and morphology of the fast-charged graphite. By applying a resting process, we scrutinize the further reactions of the plated Li, which readily transforms into irreversible (dead) Li. We further develop a modified graphite electrode with a thin Ag coating as the Li reservoir. The plated Li can be "absorbed" by the Ag layer to form the Li-Ag solid solution that suppresses the formation of dead Li and provides structural stability, thus promoting the further lithiation of graphite and enhancing the reversibility. Here this work not only provides additional insights into the fast charging behavior of graphite electrode but also demonstrates a potential strategy to improve the fast charging performance of graphite anode.

25 ENERGY STORAGE↗
NASA NTRS2021

Tunable Pseudocapacitive Intercalation of Chloroaluminate Anions into Graphite Electrodes for Rechargeable Aluminum Batteries

Rechargeable aluminum-graphite batteries using chloroaluminate-containing electrolytes have been the focus of significant research, particularly due to their high-rate capabilities. Engineered graphite electrodes have been shown to exhibit supercapacitor-like rate performance, despite the fact they store charge via the electrochemical intercalation of polyatomic AlCl4− anions. However, the origins of such rate capabilities are not well understood. Here, using electrochemical techniques, we disentangle quantitatively the diffusion-limited Faradaic, pseudocapacitive, and capacitive contributions to charge storage, revealing that AlCl4− anions intercalate into graphite with significant pseudocapacitive characteristics due to low ion diffusion limitations. Pristine and mildly exfoliated graphites are compared, where exfoliation resulted in significantly higher pseudocapacitive AlCl4− intercalation at the highest potential redox pair as well as higher galvanostatic capacity retention at faster discharge rates. The relationships between graphite structure, ion mass transport, and the overall rate of electrochemical AlCl4− intercalation are discussed. Ion diffusion within the electrolyte phase of the porous electrode is shown to play a key role in controlling the rate of intercalation at higher potentials and faster rates, which can be enhanced by reducing electrode tortuosity. The results establish that chloroaluminate anion intercalation into graphite exhibits non-diffusion-limited pseudocapacitive contributions that are tunable by modifying the graphite structure.

Jeffrey H. Xu↗
DOE OSTI2020

A High-Energy NASICON-Type Cathode Material for Na-Ion Batteries

Over the last decade, Na-ion batteries have been extensively studied as low-cost alternatives to Li-ion batteries for large-scale grid storage applications; however, the development of high-energy positive electrodes remains a major challenge. Materials with a polyanionic framework, such as Na superionic conductor (NASICON)-structured cathodes with formula Na x M 2 (PO 4 ) 3 , have attracted considerable attention because of their stable 3D crystal structure and high operating potential. Herein, a novel NASICON-type compound, Na 4 MnCr(PO 4 ) 3 , is reported as a promising cathode material for Na-ion batteries that deliver a high specific capacity of 130 mAh g –1 during discharge utilizing high-voltage Mn 2+/3+ (3.5 V), Mn 3+/4+ (4.0 V), and Cr 3+/4+ (4.35 V) transition metal redox. In addition, Na 4 MnCr(PO 4 ) 3 exhibits a high rate capability (97 mAh g –1 at 5 C) and excellent all-temperature performance. In situ X-ray diffraction and synchrotron X-ray diffraction analyses reveal reversible structural evolution for both charge and discharge.

25 ENERGY STORAGE↗
DOE OSTI2020

Lithium Manganese Spinel Cathodes for Lithium-Ion Batteries

Spinel LiMn 2 O 4 , whose electrochemical activity was first reported by Professor John B. Goodenough’s group at Oxford in 1983, is an important cathode material for lithium-ion batteries, which attracts continuous academic and industrial interests. It is cheap and environmentally friendly, and has excellent rate performance with 3-dimensional (3D) Li + diffusion channels. However, it suffers from severe degradations, especially under extreme voltages and during high-temperature operations. In this review, the current understanding and future trends of the spinel cathode and its derivatives with cubic lattice symmetry (LiNi 0.5 Mn 1.5 O 4 that shows high-voltage stability, and Li-rich spinels that show reversible hybrid anion- and cation-redox activities) shall be discussed. Special attention is given to the degradation mechanisms, further development of spinel cathodes, and concepts of utilizing the cubic spinel structure to stabilize high-capacity layered cathodes and as robust framework for high-rate electrodes. Lastly, “Good spinel” surface phases like LiNi 0.5 Mn 1.5 O 4 are distinguished from “bad spinel” surface phases like Mn 3 O 4 .

25 ENERGY STORAGE↗
DOE OSTI2021

Utilizing Oxygen Redox in Layered Cathode Materials from Multiscale Perspective

We report in high-capacity layered oxide cathode materials, utilization of lattice oxygen as a redox center is considered to be one of the most promising approaches to overcome the capacity limitation set by conventional transition metal redox centers. However, rapid material degradation is often associated with oxygen oxidation, leading to formidable challenges in utilizing oxygen redox. Further mechanistic understanding of the oxygen activities thus becomes critical to better control oxygen redox reactions. This review summarizes recent advances for investigating oxygen redox reactions in cathode materials from a multiscale perspective, i.e., from the atomistic level to the microstructure regime. First the mechanistic aspects of oxygen redox and the consequences of this reaction on various electrode degradation pathways during battery operation (e.g., oxygen loss, transition metal migration, irreversible phase transition), relating structural changes at the crystallographic scale to those at the macro scale, are discussed. Then recent developments based on atomic and microstructure modifications that are promising for improving the reversibility of oxygen redox reaction or mitigating the harmful processes arising from oxidation of the oxygen centers under high operating voltage are recounted. The analysis is concluded with a commentary on further research directions toward optimizing the oxygen activity for high-capacity charge storage.

25 ENERGY STORAGE↗
DOE OSTI2021

Super Flexible Transparent Conducting Oxide-Free Organic–Inorganic Hybrid Perovskite Solar Cells with 19.01% Efficiency (Active Area=1 cm 2 )

Highly efficient organic-inorganic hybrid perovskite solar cells (OIHP-SCs) are often fabricated on a transparent conducting oxide (TCO) substrate such as indium tin oxide (ITO). However, the presence of TCOs is disadvantageous to the development of flexible OIHP-SCs due to the brittle nature of ITO which is easily breakable during bending. Herein, a flexible TCO-free OIHP-SC is demonstrated by using lithium bis(trifluoromethane)sulfonimide (Li-TFSI) as a codopant for the single-layer graphene transparent conducting electrode and poly(triarylamine) hole-transporting material (HTM) on a flexible polydimethylsiloxane substrate. The optical and electrical properties of the Li-TFSI-doped graphene substrate are measured by controlling the doping amount and the best conditions for charge extraction are established at a doping concentration of 20 mm Li-TFSI, thus optimizing the device photovoltaic performance. As a result, a highest power conversion efficiency of 19.01% is demonstrated by the flexible TCO-free OIHP-SC devices with an active area of 1 cm 2 . In addition, the flexible TCO-free OIHP-SCs exhibit good bending stability after 5000 bending cycles at radii of 6, 4, and 2 mm and excellent light soaking stability under 1 Sun light intensity over 1000 h as opposed to the poor stability when using poly(3,4-ethylenedioxythiophene) polystyrene sulfonate as the HTM.

14 SOLAR ENERGY↗
DOE OSTI2026

Intramolecular redox-site interplay effect on organic electrode for fast-charging and wide-temperature-range sodium-ion batteries

Organic electrode materials (OEMs) hold great promise for sodium-ion batteries (SIBs) due to their exceptional structural tunability and sustainability. However, the development of OEMs with fast redox kinetics and robust structural integrity remains challenging, especially over a wide temperature range. Herein, we propose an effective strategy to address both sluggish redox kinetics and insufficient structural stability in OEMs by constructing an intramolecular redox-site interplay effect. This effect is demonstrated by two hexaazatrinaphthylene-carboxylate isomers, namely HATN-m-COONa and HATN-o-COONa. Systematic experimental and computational results jointly reveal the intramolecular redox-site interplay effect in HATN-o-COONa decreases the rigid π-π stacking interactions and minimizes the skeleton structural distortion, offering faster redox kinetics and enhanced structural integrity in HATN-o-COONa compared to HATN-m-COONa (without intramolecular redox-site interplay effect). Consequently, HATN-o-COONa exhibits superior rate performance (258 mA h g−1 at 10 A g−1) and enhanced cycle stability (93% after 1000 cycles at 5 A g−1) compared to HATN-m-COONa. More importantly, HATN-o-COONa demonstrates exceptional wide-temperature adaptability, ranging from -40 °C (315 mA h g−1 at 0.1 A g−1) to 60 oC (343 mAh g-1 at 5 A g-1). This work establishes a promising design rationale for developing fast-charging and wide-temperature adaptable OEMs for energy storage systems.

Gao, Yawei [ORNL] (ORCID:0000000225672853)↗
DOE OSTI2022

Failure analysis and design principles of silicon-based lithium-ion batteries using micron-sized porous silicon/carbon composite

Significant progresses have been made to overcome the fundamental challenges in silicon (Si)-based lithium-ion batteries (LIBs). However, much less work have been reported on the design and failure analysis these batteries for practical applications. In this work, we analyzed various cell design parameters affecting the performance of pouch cells using micron-sized porous Si with nano-pore structure and coated by pitch-carbon (p-Si/C). The correlation among particle level, electrode level, and cell level properties, especially the effect of electrode density on the volumetric capacity density of Si anode and full batteries have been systematically investigated. It is found that the corrosion of p-Si/C particle surface is the main failure mechanisms on the eventual capacity loss, while Li plating on anode electrode surface is the main reason for the fast capacity loss in later stage of cycling. The volumetric capacity of Si anode highly depends on both electrode density and the Si content. Moreover, the prelithiation of Si anodes is found to increase energy density while decreasing cycle life of Si-based full cells. Finally, the pathways and strategies for adoption of micron-sized p-Si/C anodes in LIBs have been proposed for their practical applications.

25 ENERGY STORAGE↗
DOE OSTI2022

Quantification of electrochemical-mechanical coupling in lithium-ion batteries

Lithium-ion battery safety and durability by nature are dependent on electrochemical and mechanical coupling. Interdisciplinary efforts are required to understand and quantify coupling behaviors. Here we design and conduct mechanically constrained charge and discharge characterizations with efforts supported by multiphysics modeling to unravel the coupling mechanisms of solid-liquid electrode-electrolyte and solid-solid active materials in lithium-ion batteries. We demonstrate that a lithium-ion battery cell under mechanical constraint exhibits a higher voltage during charging and a shorter charging time because of increased electrolyte resistance and decreased diffusivity caused by decreased electrode porosity. The reaction force response of the cell is a combined result of the cell structural response mechanically and lithium-ion intercalation/de-intercalation-induced volume variation electrochemically. Under mechanical constraint, cell capacity is significantly reduced in fast-charge scenarios; however, it can be recovered by a constant-voltage charge protocol. The results highlight the promise of multiphysics approaches to unravel the electrochemical-mechanical coupling mechanisms to direct battery system design and management.

25 ENERGY STORAGE↗
DOE OSTI2020

Rapid and Efficient Arsenic Removal by Iron Electrocoagulation Enabled with in Situ Generation of Hydrogen Peroxide

Millions of people are exposed to toxic levels of dissolved arsenic in groundwater used for drinking. Iron electrocoagulation (FeEC) has been demonstrated as an effective technology to remove arsenic at an affordable price. However, FeEC requires long operating times (~hours) to remove dissolved arsenic due to inherent kinetics limitations. Air cathode Assisted Iron Electrocoagulation (ACAIE) overcomes this limitation by cathodically generating H 2 O 2 in situ. In ACAIE operation, rapid oxidation of Fe(II) and complete oxidation and removal of As(III) are achieved. Here, we compare FeEC and ACAIE for removing As(III) from an initial concentration of 1464 μg/L, aiming for a final concentration of less than 4 μg/L. We demonstrate that at short electrolysis times (0.5 min), i.e., high charge dosage rates (1200 C/L/min), ACAIE consistently outperformed FeEC in bringing arsenic levels to less than WHO-MCL of 10 μg/L. Using XRD and XAS data, we conclusively show that poor arsenic removal in FeEC arises from incomplete As(III) oxidation, ineffective Fe(II) oxidation and the formation of Fe(II–III) (hydr)oxides at short electrolysis times (<20 min). Finally, we report successful ACAIE performance (retention time 19 s) in removing dissolved arsenic from contaminated groundwater in rural California.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Electron Spin Polarization and Rectification Driven by Chiral Perylene Diimide-Based Nanodonuts

The chirality-induced spin selectivity (CISS) effect allows thin-film layers of chiral conjugated molecules to function as spin filters at ambient temperature. Through solvent-modulated dropcasting of chiral l- and d-perylene diimide (PDI) monomeric building blocks, two types of aggregate morphologies, nanofibers and nanodonuts, may be realized. Spin-diode behavior is evidenced in the nanodonut structures. Stacked PDI units, which form the conjugated core of these nanostructures, dominate the nanodonut–Au electrode contact; in contrast, the AFM tip contacts largely the high-resistance solubilizing alkyl chains of the chiral monomers that form these nanodonuts. Current–voltage responses of the nanodonuts, measured by magnetic conductive AFM (mC-AFM), demonstrate substantial spin polarizations as well as spin current rectification ratios (>10) that exceed the magnitudes of those determined to date for other chiral nanoscale systems. Furthermore, these results underscore the potential for chiral nanostructures, featuring asymmetric molecular junctions, to enable CISS-based nanoscale spin current rectifiers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Coordination-Dependent Chemical Reactivity of TFSI Anions at a Mg Metal Interface

Charge transfer across the electrode–electrolyte interface is a highly complex and convoluted process involving diverse solvated species with varying structures and compositions. Despite recent advances in in situ and operando interfacial analysis, molecular specific reactivity of solvated species is inaccessible due to a lack of precise control over the interfacial constituents and/or an unclear understanding of their spectroscopic fingerprints. However, such molecular-specific understanding is critical to the rational design of energy-efficient solid–electrolyte interphase layers. We have employed ion soft landing, a versatile and highly controlled method, to prepare well-defined interfaces assembled with selected ions, either as solvated species or as bare ions, with distinguishing molecular precision. Equipped with precise control over interfacial composition, we employed in situ multimodal spectroscopic characterization to unravel the molecular specific reactivity of Mg solvated species comprising (i.e., bis(trifluoromethanesulfonyl)imide, TFSI – ) anions and solvent molecules (i.e., dimethoxyethane, DME/G1) on a Mg metal surface relevant to multivalent Mg batteries. In situ multimodal spectroscopic characterization revealed higher reactivity of the undercoordinated solvated species [Mg-TFSI-G1] + compared to the fully coordinated [Mg-TFSI-(G1) 2 ] + species or even the bare TFSI – . These results were corroborated by the computed reaction pathways and energy barriers for decomposition of the TFSI – within Mg solvated species relative to bare TFSI – . Finally, we evaluated the TFSI reactivity under electrochemical conditions using Mg(TFSI) 2 –DME-based phase-separated electrolytes representing different solvated constituents. Based on our multimodal study, we report a detailed understanding of TFSI – decomposition processes as part of coordinated solvated species at a Mg-metal anode that will aid the rational design of improved sustainable electrochemical energy technologies.

25 ENERGY STORAGE↗
DOE OSTI2020

Distinct Surface and Bulk Thermal Behaviors of LiNi 0.6 Mn 0.2 Co 0.2 O 2 Cathode Materials as a Function of State of Charge

Understanding how structural and chemical transformations take place in particles under thermal conditions can inform designing thermally robust electrode materials. Such a study necessitates the use of diagnostic techniques that are capable of probing the transformations at multiple length scales and at different states of charge (SOC). In this study, the thermal behavior ofLiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC-622) was examined as a function of SOC, using an array of bulk and surface-sensitive techniques. In general, thermal stability decreases as lithium content is lowered and conversion in the bulk to progressively reduced metal oxides (spinels, rock salt) occurs as the temperature is raised. Hard X-ray absorption spectroscopy (XAS) and X-ray Raman spectroscopy (XRS) experiments, which probe the bulk, reveal that Ni and Co are eventually reduced when partially delithiated samples (regardless of the SOC) are heated, although Mn is not. Surface-sensitive synchrotron techniques, such as soft XAS and transmission X-ray microscopy (TXM), however, reveal that for 50% delithiated samples, apparent oxidation of nickel occurs at particle surfaces under some circumstances. This is partially compensated by reduction of cobalt but may also be a consequence of redistribution of lithium ions upon heating. TXM results indicate the movement of reduced nickel ions into particle interiors or oxidized nickel ions to the surface or both. These experiments illustrate the complexity of the thermal behavior of NMC cathode materials. The study also informs the importance of investigating the surface and bulk difference as a function of SOC when studying the thermal behaviors of battery materials.

25 ENERGY STORAGE↗
DOE OSTI2022

Self-organized patterns at the plasma–liquid anode interface in a helium glow discharge: temporal development and mechanisms

Self-organization at the plasma–liquid anode interface is a commonly observed phenomenon for atmospheric pressure glow plasmas, resulting in patterns with distinctive shapes such as circular ring, star-shaped, and gear-like structures, depending primarily on the discharge current and solution conductivity. Recent studies have shown that the electrode gap distance, solute used for liquid anode solution, and gas composition can also significantly impact pattern formation. Nonetheless, an overarching model or explanation of the key underlying mechanisms consistent with all experimentally observed trends is not yet reported. We propose a key underlying mechanism enabling pattern formation motivated by a detailed parametric study of pattern formation complemented by the temporal development of patterns and consistent with all observed trends. Pattern formation was observed to be on a time scale of 100 μs, similar to the time scales of gas heating and evaporation. It was found that a minimum water evaporation rate of (3.5 ± 0.5) × 10 –6 kg s –1 and reduced electric field in the positive column of 16.6 ± 0.4 Td is required for pattern formation in the investigated cases irrespective of solution conductivity and gas composition for NaCl solutions. Nonetheless, the presence of cations for which the corresponding metal atom has a low ionization energy was identified as a necessary condition for pattern formation. Furthermore, the reported results suggest that the presence of a small amount of metal atoms in the gas phase with low ionization energy enhances the overall ionization rate in the near anode region which triggers pattern formation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1987

Investigation of a GaAlAs Mach-Zehnder electro-optic modulator

A GaAs modulator operating at 0.78 to 0.88 micron wavelength has the potential to be integrated with a GaAs/GaAlAs laser diode for an integrated fiber-optic transmitter. A travelling-wave Mach-Zehnder modulator using the electro-optic effect of GaAs and operating at a wavelength of 0.82 microns has been investigated for the first time. A four layer Strip-loaded ridge optical waveguide has been analyzed using the effective index method and single mode waveguides have been designed. The electro-optic effect of GaAs has also been analyzed and a modulator using the geometry producing the maximum phase shift has been designed. A coplanar transmission line structure is used in an effort to tap the potentially higher bandwidth of travelling-wave electrodes. The modulator bandwidth has been calculated at 11.95 GHz with a required drive power of 2.335 Watts for full intensity modulation. Finally, some preliminary experiments were performed to characterize a fabrication process for the modulator.

Materna, David M.↗
NASA NTRS1991

Electron tunnel sensor technology

Researchers designed and constructed a novel electron tunnel sensor which takes advantage of the mechanical properties of micro-machined silicon. For the first time, electrostatic forces are used to control the tunnel electrode separation, thereby avoiding the thermal drift and noise problems associated with piezoelectric actuators. The entire structure is composed of micro-machined silicon single crystals, including a folded cantilever spring and a tip. The application of this sensor to the development of a sensitive accelerometer is described.

Kenny, T. W.↗
DOE OSTI2023

Electrochemical cells for hydrogen gas production and electricity generation, and related systems and methods

An electrochemical cell comprises a first electrode, a second electrode, and a proton-conducting membrane between the first electrode and the second electrode. The first electrode comprises Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ , wherein 0≤x≤0.9, 0≤y≤0.9, 0≤z≤0.9, and δ is an oxygen deficit. The second electrode comprises a cermet material including at least one metal and at least one perovskite. Related structures, apparatuses, systems, and methods are also described.

Ding, Dong↗