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DOE OSTI2025

Temperature-Dependent Speciation of Ni(II) in Molten Chloride, Bromide, and Iodide Salts

Understanding the fundamental speciation and local structure of metal cations─such as nickel, which is present as a corrosion product─in molten salt media is essential for assessing their impact on the thermal and physical properties of salts used for advanced nuclear energy applications. In this study, we employed an integrated approach of combining X-ray absorption spectroscopy (XAS), UV–vis spectroscopy, and ab initio molecular dynamics (AIMD) to investigate the halide-dependent speciation of divalent nickel ions, Ni(II), in LiCl–KCl, LiBr–KBr, and LiI–KI eutectic salt mixtures from room temperature to 600 °C. Our findings show that both halide type and temperature significantly influence the local coordination of nickel in these molten salt systems. A notable aspect of Ni(II) speciation in LiI–KI salts is the formation of a polyiodide species. In conclusion, our findings provide critical insights into metal ion speciation in molten salt systems, enhancing our understanding of the factors that govern the physicochemical properties of these complex fluids.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Scintillator-based Timepix3 detector for neutron spin-echo techniques using intensity modulation

A scintillator-based Timepix3 (TPX3) detector was developed to resolve the high-frequency modulation of a neutron beam in both spatial and temporal domains, as required for neutron spin-echo experiments. In this system, light from a scintillator is manipulated with an optical lens and is intensified using an image intensifier, making it detectable with the TPX3 chip. Two different scintillators, namely, 6 LiF:ZnS(Ag) and 6 LiI:Eu, were investigated to achieve the high resolution needed for spin-echo modulated small-angle neutron scattering (SEMSANS) and modulation of intensity with zero effort (MIEZE). The methodology for conducting event-mode analysis is described, including the optimization of clustering parameters for both scintillators. The detector with both scintillators was characterized with respect to detection efficiency, spatial resolution, count rate, uniformity, and γ-sensitivity. The 6 LiF:ZnS(Ag) scintillator-based detector achieved a spatial resolution of 200 μm and a count rate capability of 1.1 × 10 5 cps, while the 6 LiI:Eu scintillator-based detector demonstrated a spatial resolution of 250 μm and a count rate capability exceeding 2.9 × 10 5 cps. Furthermore, high-frequency intensity modulations in both spatial and temporal domains were successfully observed, confirming the suitability of this detector for SEMSANS and MIEZE techniques, respectively.

47 OTHER INSTRUMENTATION↗

DOE OSTI2026

Comparing Thermal Neutron Scintillators for Use With SiPM-Readout Detectors

Scintillator-based thermal neutron detectors for scientific scattering facilities offer an effective combination of large-area coverage and good spatial resolution. At Oak Ridge National Laboratory, silicon photomultiplier (SiPM)-readout Anger cameras using 6 Li glass scintillators have been developed, but the spatial resolution of these detectors is limited by the relatively low light yield of the glass. Recently, several brighter scintillator compositions with sufficient 6 Li concentration have emerged as promising candidates for higher-resolution imaging. Here, in this work, we evaluate five scintillator materials: GS20, LiF/ZnS:Ag, LiF/ZnO:Zn, LiI:Eu, and Cs 2 LiYCl 6 :Ce, each mounted on a SiPM Anger camera. For each scintillator, the neutron detection efficiency, spatial resolution, and count rate capabilities were measured and compared. Each of the new compositions achieved a spatial resolution better than 0.5 mm, compared to 0.66 mm for GS20, with LiI:Eu reaching the best value of 0.32 mm. Although these compositions improve the spatial resolution of the Anger camera, their longer pulse decay times limit their use in high count rate applications, and the camera’s hardware must be optimized for the different properties of the new scintillators.

Neutron detectors↗

DOE OSTI2021

Self-Healing, Improved Efficiency Solid State Rechargeable Li/I 2 Based Battery

Solid state electrolytes are receiving significant interest due to the prospect of improved safety, however, addressing the incidence and consequence of internal short circuits remains an important issue. In this study, a battery based on a LiI-LiI(HPN) 2 solid state electrolyte demonstrated self-healing after internal shorting where the cells recovered and continued to cycle effectively. The functional rechargeable electrochemistry of the self-forming Li/I 2 -based battery was investigated through interfacial modification by inclusion of Li metal (at the negative interface), and/or fabricated carbon nanotube substrates at the positive interface. A cell design with lithium metal at the negative and a carbon substrate at the positive interface produced Coulombic efficiencies > 90% over 60 cycles. Finally, the beneficial effects of moderately elevated temperature were established where a 10 °C temperature increase led to ~5× lower resistance.

25 ENERGY STORAGE↗

DOE OSTI2021

Chemical Heterogeneity in PAN/LLZTO Composite Electrolytes by Synchrotron Imaging

Solid polymer/ceramic composite electrolytes are promising for batteries due to their attractive thermal stability and mechanical properties. Chemical heterogeneity in solid composite electrolytes, such as the inhomogeneity in the ceramic phase and salt distribution at the polymer/ceramic interface, is critical to the performance of solid composite electrolytes. However, such heterogeneity has not been well understood yet. In this work, we use Synchrotron-based X-ray fluorescence imaging (XRF) and Transmission X-ray Microscope (TXM) to image nanoscale chemical heterogeneity in polyacrylamide/Li 7+x La 3 Zr 2–x Ta x O 12 (LLZTO) composite electrolytes and investigate the effects of lithium salt, salt concentration, and plasticizer. We find that LLZTO particles show strong inter- and intra-particles chemical heterogeneities, and the off-stoichiometry of Zr in an LLZTO particle is unlikely to be only balanced by Ta substitution. Moreover, statistical analysis suggests that LiI tends to accumulate at the ceramic/polymer interface at a low concentration of 5 wt%, but no such tendency was observed in samples with 10 wt% LiI. However, composite electrolytes with LiTFSI show interfacial accumulation at both 5 wt% and 10 wt%. Furthermore, this report provides insight into element distributions in solid composite electrolytes, and we hope further researches can shed light on the connections between chemical heterogeneity and ionic transport pathway inside.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Moisture Stability of Sulfide Solid-State Electrolytes

In this report we detail a comprehensive study on the moisture stability of sulfide solid-state electrolytes in dry room environments. Although sulfide SSEs have many favorable attributes, this class of materials suffers from poor stability with water. Sulfide SSEs react with water to form gaseous H 2 S and a variety of solid byproducts like Li 3 PO 4 and LiOH, which go on to increase the interfacial impedance of solid-state batteries. Lab-scale research typically utilizes gloveboxes with <1 ppm water, however, the large-scale manufacturing of Li-ion batteries occurs in –40°C dewpoint dry rooms with around 126 ppm water. Consequently, the moisture stability of sulfide SSEs must be addressed if the manufacture of solid-state batteries based on sulfide SSEs is to be scaled up. Here, we are the first to characterize the moisture stability of sulfide SSEs according to both H 2 S and the degradation of ionic conductivity at different moisture setpoints ranging from –76°C to –40°C dewpoint. A variety of different SSE compositions are studied; namely, (Li 2 S) 75 (P 2 S 5 ) 25 , (Li 2 S) 70 (P 2 S 5 ) 30 , (Li 2 O) 7 (Li 2 S) 68 (P 2 S 5 ) 25 , (Li 2 O) 7 (Li 2 S) 63 (P 2 S 5 ) 30 , and (Li 2 S) 75 (P 2 S 5 ) 25 + 20 mol% LiI. We find that moisture stability improves with 75 mol% Li2S modifier content and the introduction of a Li 2 O co-modifier. After a 30 min exposure in a –40°C dewpoint dry room environment we found that (Li 2 S) 75 (P 2 S 5 ) 25 + 20 mol% LiI powder generated 0.1 cc/g H 2 S and its ionic conductivity decreased by over 50%. However, when SSE powder was exposed as a slurry in a dodecane carrier the same SSE composition generated 0 cc/g H 2 S and its ionic conductivity only dropped by 14%. Our results show that sulfide SSEs have acceptable moisture stability when appropriately processed in a dry room environment.

25 ENERGY STORAGE↗

DOE OSTI2022

Laser diagnostics to characterize the in-flame growth of platinum nanoparticles manufactured by the reactive spray deposition technology

Reactive Spray Deposition Technology (RSDT) is an atmospheric pressure, flame-based advanced manufacturing method used to fabricate Membrane Electrode Assemblies (MEAs) for proton exchange fuel cells and water electrolyzers. RSDT combines the flame synthesis of catalyst nanoparticles and their deposition onto the membrane in one step. The properties of the synthesized nanoparticles, such as their Size Distribution Function (SDF), determine the manufactured electrodes’ performance, which can be evaluated when the deposition is complete via ex-situ characterization of the products. Efforts to improve RSDT for manufacturing state-of-the-art MEAs can be significantly enhanced with integrated laser diagnostics that enable in situ measurement of the synthesized catalyst nanoparticles. This paper reports the implementation of laser diagnostics in an RSDT facility and evaluates their potential to assist the manufacturing process. Laser Light Scattering (LS) and Laser-Induced Incandescence (LII) measurements are performed in the oxygen-rich zone of the flame at various distances from the flame fuel jet nozzle downstream of its luminous region. The measurements quantitatively track the evolution in size and volume fraction of platinum-based nanoparticles in two flames that yield different catalytic properties in the manufactured electrodes. The profiles of the measured nanoparticles’ volume fraction along the flame axis can be estimated a priori so that the average nanoparticle sizes can be measured in quasi-real time via LS. Nanoparticles experience an extremely slow growth rate while being convected at distances from 150 nm to 300 nm from the fuel nozzle. Complementary characterizations of the synthesized nanoparticles are performed ex-situ via High-Angle Annular Darkfield Scanning Transmission Electron Microscopy (HAADF-STEM) image analyses of samples collected on grids at a fixed distance from the fuel jet nozzle. Comparing the results from laser and microscopy techniques not only cross-validates the findings but also provides the parameters to infer the bimodal SDF in-situ and yields evidence that the coagulation efficiency of the synthesized nanoparticles has extremely low values in the investigated zone of the flames.

Rayleigh Light Scattering (LS)↗

DOE OSTI2023

Pulsed laser heating of diesel engine and turbojet combustor soot: Changes in nanostructure and implications

Here, carbonaceous particulate produced by a diesel engine and turbojet engine combustor are analyzed by transmission electron microscopy (TEM) for differences in nanostructure before and after pulsed laser annealing. Soot is examined between low/high diesel engine torque and low/high turbojet engine thrust. Small differences in nascent nanostructure are magnified by the action of high-temperature annealing induced by pulsed laser heating. Lamellae length distributions show occurrence of graphitization while tortuosity analyses reveal lamellae straightening. Differences in internal particle structure (hollow shells versus internal graphitic ribbons) are interpreted as due to higher internal sp3 and O-atom content under the higher power conditions with hypothesized greater turbulence and resulting partial premixing. TEM in concert with fringe analyses reveal that a similar degree of annealing occurs in the primary particles in soot from both diesel engine and turbojet engine combustors—despite the aggregate and primary size differences between these sources. Implications of these results for source identification of the combustion particulate and for laser-induced incandescence (LII) measurements of concentration are discussed with inter-instrument comparison of soot mass from both diesel and turbojet soot sources.

42 ENGINEERING↗

DOE OSTI2025

Computational and experimental analysis of structural and Thermophysical properties of LiX-KX (X = chloride, iodide, or bromide) molten salts

Molten salts containing lithium (Li) and potassium (K) halides, including chlorides (Cl), bromides (Br), and iodides (I), are pivotal in advanced technological applications including nuclear reactor technologies, thermal batteries, and industrial pyrochemical processes. Despite their significance, the availability of the temperature-dependent structural and thermophysical properties of these molten salts remain scarce. Here, this study addresses this knowledge gap by predicting and measuring the key properties such as coordination number, radial distribution function, density, heat capacity, and volumetric thermal expansion of molten LiI-KI, LiBr-KBr and LiCl-KCl eutectic mixtures. Utilizing ab initio molecular dynamics (AIMD) simulations, we predict these properties of LiX-KX (X=Br,I, Cl) across various temperatures, with chlorides as a benchmark. Experimental measurements using Archimedes methods and Differential Scanning Calorimetry validate the densities and heat capacities of these molten salts. Our comprehensive analysis of the structural and thermophysical properties provides critical insights into the behavior of these molten salts at various temperatures, enhancing the understanding necessary for their application in advanced technologies.

36 - MATERIALS SCIENCE↗

DOE OSTI2020

Influence of Added Salt on Chain Conformations in Poly(ethylene oxide) Melts: SANS Analysis with Complications

Poly(ethylene oxide) (PEO)-based electrolytes have gained increasing attention in both the rechargeable battery industry and fundamental research, but any influence of the ions on the polymer conformation is not fully understood. Small-angle neutron scattering (SANS) is a powerful means to determine single-polymer chain conformations. We conducted SANS experiments on 50:50 blends of perdeuterated PEO (dPEO) and hydrogenous PEO (hPEO) of two different molecular weights (20 and 40 kDa) doped with two different salts (LiTFSI and LiClO 4 ) at various concentrations. An additional measurement with LiI is also reported. The scattering profiles of salt-doped dPEO/hPEO blends were measured, and the incoherent scattering from dPEO and hPEO doped with salt was measured separately. A strong low q upturn was observed in some of the blends and in the pure dPEO homopolymers. The statistical segment lengths of PEO–salt mixtures were derived using a Kratky analysis. The segment length decreases modestly with increasing amounts of LiTFSI but apparently first increases then decreases with added LiClO 4 . At the highest salt concentration examined (r = [Li+]/[EO] = 0.125), a roughly 10% decrease in the statistical segment length was observed in both LiTFSI and LiClO 4 -doped PEOs, for both molecular weights. This work confirms that added salt causes a contraction of the PEO chain dimensions, but the effect appears slightly weaker than reported recently. Certain difficulties in data analysis are also discussed, including the unexplained low q scattering even in pure deuterated polymers, uncertainties in background subtraction, and inappropriate application of the Debye function.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Hydride-Based Interlayer for Solid-State Anode-Free Battery

Solid-state batteries (SSBs) are considered a promising approach to realizing an anode-free concept with high energy densities. However, the initial Coulombic efficiency (ICE) has remained insufficient for anode-free batteries using sulfide-based solid electrolytes (SEs). Herein, we incorporated a hydride-based interlayer, 3LiBH 4 -LiI (LBHI), between a typical sulfide SE, Li 6 PS 5 Cl, and the Cu current collector. Further, by investigating the Li plating and stripping behaviors and the (electro)chemical stability between SEs and plated Li, we demonstrated that LBHI can effectively improve interfacial stability, leading to an ICE exceeding 94% in anode-free half cells. This interlayer also improves Coulombic efficiencies and specific capacities in anode-free full cells. Furthermore, the utilization of LBHI enables one to study Li plating behaviors without interference from interfacial (electro)chemical instabilities. The analysis of stack pressure evolution during electrochemical cycling reveals that soft shorting in SSBs arises from both dendrite formation and deformation, offering insights into further optimizing solid-state anode-free batteries.

25 ENERGY STORAGE↗

DOE OSTI2023

Structural mapping and tuning of mixed halide ions in amorphous sulfides for fast Li-ion conduction and high deformability

Amorphous sulfides are among the most promising candidates for solid electrolytes (SEs) owing to their excellent deformability and acceptable Li-ion conductivity (σion) at room temperature. However, the complex atomic structure of these amorphous materials without long-range ordering results in a lack of structural understanding and difficulties in tuning material properties. Here, in this study, we performed structural mapping of glassy sulfide SEs composed of various anion clusters using a combinatorial atomic level analysis of synchrotron X-ray-based pair distribution function (PDF) and reverse Monte-Carlo (RMC) methods, demonstrating the potential to tune σ ion in glass SEs. First, we prepared a new glassy sulfide with a mixed anion framework of two halogens (Br and I) as atomic anions, with PS 4 3- molecular anions in a Li 2 S–P 2 S 5 -based glass SE. At a specific Br content, [(Li 2 S) 0.658 (LiI 0.9 LiBr 0.1 ) 0.342 ] 0.825 [P 2 S 5 ] 0.175 recorded a σ ion of 2.27 mS cm -1 , the highest value for any glass sulfides reported to date; however, its elastic modulus was still suppressed to 14.48 GPa. PDF and RMC calculations successfully provided structural mapping of anion clusters, including two halogens. Molecular dynamics simulations of each composition confirmed that flexible coordination caused by the rattling of small polarizable Br ions in the mixed halogens of glassy SEs contributed to the superior σ ion . Our results may provide new insights into the design of superior glassy SEs that play key roles in all-solid-state batteries requiring fast Li-ion conduction and high deformability.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Calibration sources for the LEGEND-200 experiment

In the search for a monochromatic peak as the signature of neutrinoless double beta decay an excellent energy resolution and an ultra-low background around the Q-value of the decay are essential. The LEGEND-200 experiment performs such a search with high-purity germanium detectors enriched in 76 Ge immersed in liquid argon. To determine and monitor the stability of the energy scale and resolution of the germanium diodes, custom-made, low-neutron emission 228 Th sources are regularly deployed in the vicinity of the crystals. Here we describe the production process of the 17 sources available for installation in the experiment, the measurements of their alpha- and gamma- activities, as well as the determination of the neutron emission rates with a low-background LiI(Eu) detector operated deep underground. With a flux of ( 4.27 ± 0.60 stat ± 0.92 syst ) × 10 -4 n / (kBq·s), approximately one order of magnitude below that of commercial sources, the neutron-induced background rate, mainly from the activation of 76 Ge, is negligible compared to other background sources in LEGEND-200.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Dual Function Solid State Battery with Self-Forming Self-Healing Electrolyte and Separator (Final Scientific/Technical Report)

Over the course of this program, we have demonstrated an improved rechargeable Li/I2 battery with reduced impedance, improved cyclability, improved Coulombic Efficiency, and the ability to “self-heal” during shorting events. Multi-year efforts have led to the development and improvements in the composition, fabrication, and preparation of the solid state electrolyte, the role of the interface, and design of appropriate test conditions. These investigations have led to significant improvements in Coulombic efficiency. By systematic development of a composite solid state electrolyte, this system is able to self-form upon charge, thus lending itself to long shelf life before use. The initial project objective was to demonstrate a solid-state rechargeable battery based on a Li-metal anode and iodine cathode with a self-forming, self-healing electrolyte and separator with high gravimetric and volumetric energy density. The final deliverables of this project build on a multi-year effort beginning with materials development and design to generate a suitable solid state electrolyte composite with demonstrated higher ionic conductivity compared to the baseline (LiI). Development in cell design and interface modification leading to the generation of rechargeable solid electrolyte cells with Coulombic efficiency improvements of ~3X over initial tests, as well as demonstration of self-healing behavior, where the cells retained their ability to continue extended cycling after shorting events. The hypothesis put forward as part of the initial concept for the project was that the cell chemistry would be self-healing. For example, if a lithium dendrite formed during charge of the cell and reached the iodine cathode, the reaction of the lithium dendrite with the iodine would consume the tip of the dendrite to form lithium iodide, more of the solid electrolyte. The formation of the solid electrolyte would allow the cell to recover and continue to function. This type of self-healing during cycling has been demonstrated and has the potential to improve on safety considerations that stem from shorting events in other Li- containing systems.

25 ENERGY STORAGE↗

DOE OSTI2023

Real time lithium metal calendar aging in common battery electrolytes

Li metal anodes are highly sought after for high energy density applications in both primary commercial batteries and next-generation rechargeable batteries. In this research, Li metal electrodes are aged in coin cells for a year with electrolytes relevant to both types of batteries. The aging response is monitored via electrochemical impedance spectroscopy, and Li electrodes are characterized post-mortem. It was found that the carbonate-based electrolytes exhibit the most severe aging effects, despite the use of LiBF 4 -based carbonate electrolytes in Li/CF x Li primary batteries. Highly concentrated LiFSI electrolytes exhibit the most minimal aging effects, with only a small impedance increase with time. This is likely due to the concentrated nature of the electrolyte causing fewer solvent molecules available to react with the electrode surface. LiI-based electrolytes also show improved aging behavior both on their own and as an additive, with a similar impedance response with time as the concentrated LiFSI electrolytes. Since I − is in its most reduced state, it likely prevents further reaction and may help protect the Li electrode surface with a primarily organic solid electrolyte interphase.

25 ENERGY STORAGE↗

DOE OSTI2022

Molten fluid apparatus with solid non-brittle electrolyte

A battery includes a fluid negative electrode and a fluid positive electrode separated by a solid electrolyte at least when the electrodes and electrolyte are at an operating temperature. The solid electrolyte includes ions of the negative electrode material forming the fluid negative electrode and has a softness less than beta-alumina solid electrolyte (BASE) ceramics. In one example, the fluid negative electrode comprises lithium (Li), the fluid positive electrode comprises sulfur (S) and the solid electrolyte comprises lithium iodide (LiI).

Vissers, Daniel R.↗

DOE OSTI2020

The Effect of Artificial SEIs on Lithium Metal Anode Morphology and Conductivity

Lithium metal has often been termed the “holy grail” of battery technology, due to its high capacity (2,061 mAh/cm3) and low electrochemical potential (-3.04 V vs. SHE). However, lithium’s beneficially low potential also causes it to be highly reactive in the presence of organic solvents, making it difficult to harness the high energy capabilities for rechargeable batteries. Common failure of lithium metal batteries occurs by rapid dendrite growth leading to a hazardous short-circuit. Various methods have been brought forth to better understand the fundamental mechanisms of lithium metal batteries, as well as modifications made to better stabilize lithium metal. A common route of modification is done through interface engineering, with attempts to artificially provide a stable, homogeneous solid-electrolyte interface (SEI). The stability of the SEI has direct effects on the heterogeneity of the electrode surface, which initiates a waterfall effect of for progressive reactions such as dendrite growth, dead lithium accumulation, and electrolyte consumption. This work aims to produce a mixed LiI-LiF artificial SEI to improve ionic conductivity while retaining a high elastic modulus.

25 ENERGY STORAGE↗

DOE OSTI2024

Molten fluid apparatus with solid non-brittle electrolyte

A battery includes a fluid negative electrode and a fluid positive electrode separated by a solid electrolyte at least when the electrodes and electrolyte are at an operating temperature. The solid electrolyte comprises a salt formed by ions of the negative electrode material forming the fluid negative electrode. In one example, the fluid negative electrode comprises lithium (Li), the fluid positive electrode comprises sulfur (S) and the solid electrolyte comprises lithium iodide (LiI).

Vissers, Daniel R.↗