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DOE OSTI2020

Low Threshold Voltages Electrochemically Drive Gold Migration in Halide Perovskite Devices

The constituent ions of halide perovskite materials are mobile in the solid state and known to participate in reduction/oxidation reactions. Yet few parameters related to electrochemical processes occurring within devices have been carefully determined. Here, we characterize such reactions in model MAPbI3 perovskite devices, and we quantify threshold voltages for key reactions. Gold is oxidized and mobilized under nitrogen, in the dark, at the MAPbI3/Au interface at 0.8 V. When this interface is buffered with the organic hole transport material (HTM), 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene, MAPbI3 begins to degrade at 1.2 V; degradation liberates ions that subsequently enable Au migration. Thresholds are insensitive to MAPbI3 thickness or choice of organic HTM or oxide cathode, which suggests that these reactions are driven electrochemically; the electric field across the device is less important. These results have profound implications for understanding in operando degradation pathways of optoelectronic perovskite devices that are varied in terms of interface structures, active material compositions, and ranges of external stressors.

42 ENGINEERING↗

DOE OSTI2026

Flash electropolishing for TEM: Reducing FIB‐induced defects in tungsten with protocols for new materials

Focused ion beam (FIB) milling has become the dominant approach for site-specific transmission electron microscopy (TEM) specimen preparation; however, FIB damage remains a critical limitation for reliable microstructural characterisation, particularly in radiation effects studies. Tungsten is especially susceptible to FIB damage due to its high nuclear stopping power, which promotes the formation and strong diffraction contrast of FIB-induced ‘black spot’ defects that are indistinguishable from very fine irradiation-induced loops/defects resulting from low to intermediate temperature neutron irradiation. In this work, flash electropolishing is systematically evaluated as a post-FIB treatment for minimising preparation-induced artefacts for TEM analysis of tungsten-based alloys. Using a range of non-, ion-, and neutron-irradiated tungsten materials, the effectiveness of flash electropolishing has been assessed through direct comparison with conventional FIB and plasma-FIB preparation including low-energy Ga, Ar, Xe ion cleaning. The results demonstrate that flash electropolishing effectively removes FIB-damaged layers and ‘black spot’ defects, thereby enabling reliable observation of irradiation-induced dislocation structures. Key processing parameters governing flash electropolishing quality – including lamella thickness, applied voltage, polishing duration, electrolyte chemistry, and cathode geometry – have been systematically evaluated, and clear criteria were established for determining when flash electropolishing is required to ensure reliable microstructural analysis. This work also provides practical guidance for implementing flash electropolishing as an artefact-controlled specimen-preparation approach for TEM characterisation of FIB-produced specimens. The systematic protocol can be extended to other, non-tungsten materials.

TEM sample preparation↗

DOE OSTI2025

Enhancing cathode composites with conductive alignment synergy for solid-state batteries

Enhancing transport and chemomechanical properties in cathode composites is crucial for the performance of solid-state batteries. Our study introduces the filler-aligned structured thick (FAST) electrode, which notably improves mechanical strength and ionic/electronic conductivity in solid composite cathodes. The FAST electrode incorporates vertically aligned nanoconducting carbon nanotubes within an ion-conducting polymer electrolyte, creating a low-tortuosity electron/ion transport path while strengthening the electrode’s structure. This design not only mitigates recrystallization of the polymer electrolyte but also establishes a densified local electric field distribution and accelerates the migration of lithium ions. The FAST electrode showcases outstanding electrochemical performance with lithium iron phosphate as the active material, achieving a high capacity of 148.2 milliampere hours per gram at 0.2 C over 100 cycles with substantial material loading (49.3 milligrams per square centimeter). This innovative electrode design marks a remarkable stride in addressing the challenges of solid-state lithium metal batteries.

Science & Technology - Other Topics↗

DOE OSTI2022

A Solution-Processable High-Modulus Crystalline Artificial Solid Electrolyte Interphase for Practical Lithium Metal Batteries

The solid electrolyte interphase (SEI) has been identified as a key challenge for Li metal anodes. The brittle and inhomogeneous native SEI generated by parasitic reactions between Li and liquid electrolytes can devastate battery performance; therefore, artificial SEIs (ASEIs) have been proposed as an effective strategy to replace native SEIs. Herein, as a collaboration between academia and industrial R&D teams, a multifunctional (crystalline, high modulus, and robust, Li + ion conductive, electrolyte-blocking, and solution processable) ASEI material, LiAl-FBD (where “FBD” refers to 2,2,3,3-tetra-fluoro-1,4-butanediol), for improving Li metal battery performance is designed and synthesized. The LiAl-FBD crystal structure consists of Al 3+ ions bridged by FBD 2– ligands to form anion clusters while Li + ions are loosely bound at the periphery, enabling an Li + ion conductivity of 9.4 × 10 –6 S cm –1 . Further, the fluorinated, short ligands endow LiAl-FBD with electrolyte phobicity and high modulus. The ASEI is found to prevent side reactions and extend the cycle life of Li metal electrodes. Specifically, pairing LiAl-FBD coated 50 μm thick Li with industrial 3.5 mAh cm –2 NMC811 cathode and 2.8 μL mAh –1 lean elec-trolyte, the Li metal full cells show superior cycle life compared to bare ones, achieving 250 cycles at 1 mA cm –2 .

25 ENERGY STORAGE↗

DOE OSTI2023

Dynamic Molecular Investigation of the Solid-Electrolyte Interphase of an Anode-Free Lithium Metal Battery Using In Situ Liquid SIMS and Cryo-TEM

Solid electrolyte interphase (SEI) has been widely perceived to play a critical role in the stable cycling of rechargeable batteries. However, associated with the fragile and air-sensitive nature of the SEI layer, delineation of the formation process and the nature of SEI remains a big challenge. Here, we use in situ liquid time-of-flight secondary ion mass spectroscopy (TOF-SIMS), cryo- transmission electron microscope (TEM) and density functional theory (DFT) calculation to delineate molecular process on the formation of SEI layer under the dynamic operating condition. We discover that the onset potential for SEI layer formation and the thickness of the SEI show dependence on the solvation shell structure. Using LiCoO 2 as a cathode and Cu film as an anode, the SEI is noticed to start to form at around 2.0 V and reach its final thickness (irreversible part, ~ 40-50 nm) at about 3.0 V in the 1 M LiPF 6 –EC/DMC electrolyte, while for the case of 1 M LiFSI–DME, the SEI starts to form at around 1.5 V and reaches its final thickness (~ 20 nm) at about 2.0 V. The in situ TOF-SIMS clearly indicates the outer SEI layer formation and dissipation upon charging and discharging, implying a continued evolution of electrolyte structure with extended cycling. In conclusion, the present work establishes a direct correlation between the molecular signature of SEI layer with solvation feature of electrolytes in lithium batteries, providing insights for tailoring SEI layer toward improved electrochemical properties of lithium batteries.

25 ENERGY STORAGE↗

DOE OSTI2021

Impact of electrode porosity architecture on electrochemical performances of 1 mm-thick LiFePO4 binder-free Li-ion electrodes fabricated by Spark Plasma Sintering

Thick electrodes with high active material loadings have been intensively studied over the last couple of decades in pursuit of achieving high energy density systems. To optimize and enhance the electrochemical performance of such electrodes, one has to control the pore morphology by, for example, varying the pore size and shape, and the level of porosity. In the present work, the fabrication of thick binder-free LiFePO4 (LFP) electrodes with two different pore sizes (12 and 20 mu m) and porosities (21 vol% and 44 vol%) using Spark Plasma Sintering (SPS) and templating approach is reported. The well-controlled porous architecture inside the thick electrodes is realized by fine-tuning experimental parameters. The impact of porosity architecture on electrochemical performance is quantified and correlated with the 3D tortuosity values determined from both micro-computed tomography and electrochemical impedance-based experimental methods. Based on the micro-computed tomography data analysis, estimated tortuosity values along X, Y, and Z axes reveal an anisotropic effect perpendicularly to the SPS compression axis (Z-direction). This is particularly profoundly observed in the samples with larger pores (20 mu m). The correlation between morphological properties and the rate capability performance is established indicating that the capacity loss happens mainly due to the Li-ion diffusion limitations.

Cathode material↗

DOE OSTI2025

3D printing of architected sulfur cathodes with dual-site atomic catalysts for accelerated polysulfide kinetics and Li-ion transport in high areal-loading lithium–sulfur batteries

The practical deployment of lithium–sulfur batteries (LSBs) is hindered by fundamental limitations in conventional slurry-cast cathodes, including poor sulfur utilization, sluggish ion transport, and low areal capacity, particularly in thick electrodes required for high energy density. To address these challenges, we present direct ink writing (DIW) as an additive manufacturing strategy to fabricate advanced current-collector-free, 3D-printed sulfur cathodes (3DP S@CoNi-DSACs/NC) with hierarchically porous architectures that enhance lithium-ion diffusion, promote electrolyte penetration, and reduce interfacial resistance. The synergistic effects of Co/Ni dual-atom sites accelerate redox kinetics and mitigate polysulfide shuttling. As a result, the optimized 3DP cathode with a sulfur loading of 5.4 mg cm −2 demonstrated excellent rate capability, delivering a high reversible capacity of 1041.4 mAh g −1 at 1C with 85.5% capacity retention after 1000 cycles, significantly outperforming its cast counterpart. Remarkably, even at a higher sulfur loading of 8.1 mg cm −2 , the 3DP cathode maintains outstanding performance, achieving a discharge capacity of 1538.4 mAh g −1 and an areal capacity of 12.5 mAh cm −2 at 0.1C. This study not only demonstrates the functional integration of catalytically active materials into 3D printable sulfur cathode architectures but also offers a scalable and transformative platform for building high-performance LSBs beyond conventional electrode manufacturing methods.

3D electrode↗

DOE OSTI2024

Accelerating FEM-Based Corrosion Predictions Using Machine Learning

Atmospheric corrosion of metallic parts is a widespread materials degradation phenomena that is challenging to predict given its dependence on many factors (e.g. environmental, physiochemical, and part geometry). For materials with long expected service lives, accurately predicting the degree to which corrosion will degrade part performance is especially difficult due to the stochastic nature of corrosion damage spread across years or decades of service. The Finite Element Method (FEM) is a computational technique capable of providing accurate estimates of corrosion rate by numerically solving complex differential Eqs. characterizing this phenomena. Nevertheless, given the iterative nature of FEM and the computational expense required to solve these complex equations, FEM is ill-equipped for an efficient exploration of the design space to identify factors that accelerate or deter corrosion, despite its accuracy. In this work, a machine learning based surrogate model capable of providing accurate predictions of corrosion with significant computational savings is introduced. Specifically, this work leverages AdaBoosted Decision trees to provide an accurate estimate of corrosion current per width given different values of temperature, water layer thickness, molarity of the solution, and the length of the cathode for a galvanic couple of aluminum and stainless steel.

36 MATERIALS SCIENCE↗

NASA NTRS1993

Optical and scratch resistant properties of diamondlike carbon films deposited with single and dual ion beams

Amorphous diamondlike carbon (DLC) films were deposited using both single and dual ion beam techniques utilizing filament and hollow cathode ion sources. Continuous DLC films up to 3000 A thick were deposited on fused quartz plates. Ion beam process parameters were varied in an effort to create hard, clear films. Total DLC film absorption over visible wavelengths was obtained using a Perkin-Elmer spectrophotometer. An ellipsometer, with an Ar-He laser (wavelength 6328 A) was used to determine index of refraction for the DLC films. Scratch resistance and frictional and adherence properties were determined for select films. Applications for these films range from military to the ophthalmic industries.

Kussmaul, Michael T.↗

NASA NTRS1993

Optical and Scratch Resistant Properties of Diamondlike Carbon Films Deposited with Single and Dual Ion Beams

Amorphous diamond-like carbon (DLC) films were deposited using both single and dual ion beam techniques utilizing filament and hollow cathode ion sources. Continuous DLC films up to 3000 A thick were deposited on fused quartz plates. Ion beam process parameters were varied in an effort to create hard, clear films. Total DLC film absorption over visible wavelengths was obtained using a Perkin-Elmer spectrophotometer. An ellipsometer, with an Ar-He laser (wavelength 6328 A) was used to determine index of refraction for the DLC films. Scratch resistance, frictional, and adherence properties were determined for select films. Applications for these films range from military to the ophthalmic industries.

Kussmaul, Michael T.↗

DOE OSTI2021

Townsend to glow discharge transition for a nanosecond pulse plasma in helium: space charge formation and resulting electric field dynamics

Stark polarization spectroscopy is used to investigate the temporal evolution of the electric field distribution in the cathode region of a nanosecond pulsed discharge in helium at 120 Torr. The measurements are performed on the He I transition at 492.19 nm, during the early stages of the discharge formation. The experimental results are compared with the predictions of a 1D fluid model. Time-resolved ICCD images show that the discharge develops as a diffuse, cathode-directed ionization wave with a Townsend-like feature before transitioning into a glow-like structure. Near anode instabilities characterized by filament formation were observed near the high voltage electrode. Within 30 ns, a reduction of the sheath thickness to about 250 μm is observed, coinciding with a gradual increase of the discharge current and proportional increase in electric field at the cathode. Additionally, the cathode electric field corresponding to this sheath with a thickness of 250 μm is about 40 kV cm -1 . A subsequent steep increase of the discharge current leads to a further reduction of the sheath width. The electric field evolution as obtained by the fluid model is in excellent agreement with the measurements and shows that an enhanced ionization near the cathode is causing the space charge formation responsible for the increase in electric field.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

Optimization of catholyte for halide-based all-solid-state batteries

Halide solid electrolytes gain significant attention due to their high ionic conductivity, low processing temperature, dry air compatibility, and high-voltage stability. However, low cathode active material (CAM) loading in the composite cathode constrains the realization of high energy density for halide-based all-solid-state batteries. In this study, three halide materials, raw Li 3 YBrCl 5 (LYBC-R, <30μm), milled LYBC (LYBC-M, <5 μm) and freeze-dried Li 3 InCl 6 (LIC, <500 nm), were used as catholytes, combined with LYBC-M as the electrolyte and LiIn alloy as the anode. The CAM:catholyte ratio was investigated as well as stack pressure and operating temperature. Our study demonstrates that particle size of the catholyte plays an important role only for high CAM loading or high C-rate cycling. At moderate CAM loading (65 and 70wt% LiNi 0.83 Mn 0.06 Co 0.11 O 2 ) and 0.1 C-rate, all the three catholytes perform well, providing initial discharge capacities >177 mAh/g. At high CAM loading (85wt%) and 0.1 C-rate, a cathode with the nano-scale LIC catholyte provides discharge capacity of 175 mAh/g, while the larger particle size catholytes suffer significantly reduced capacity. Both LYBC and LIC catholytes provided capacity retention >80% after 200 cycles at 0.5C. These results imply that cathode particle size is critically important for performance at high CAM loading. Furthermore, both electrolyte and cathode were tape cast to scale up size and prepare realistic layer thicknesses. A small amount of binder was used in both layers, to balance the electrochemical performance and mechanical properties. Further, the discharge capacity of a tape cell was 152mA h/g at 0.1C with a capacity retention of 81.8% after 20 cycles at 0.5C. The results demonstrate the excellent performance of LYBC as an electrolyte, and provide guidance for halide-based cathode design.

25 ENERGY STORAGE↗

NASA NTRS1991

A 5,000 hour xenon hollow cathode life test

A cathode life test voluntary terminated after 5024 hours of operation at 25 A is reported. The cathode including a 6.35-mm diameter by 57.12-mm long molybdenum tube with a nominal wall thickness of 0.38 mm is described along with a test facility and start-up procedure. It is shown that over the time of the experiment, the cathode-orifice diameter eroded from 1.80 mm to 2.08 mm, which corresponds to a ratio of the emission current to the orifice diameter at the end of the test of 12.0 A/mm. Tungsten deposits on the interior surface of the insert are detected in post-test analyses, and complete depletion of the original impregnate is suggested by X-ray diffraction analyses. A cathode-jet phenomenon in which energetic ions are produced during hollow-cathode operation at emission currents above 20 A is confirmed.

Brophy, John R.↗

DOE OSTI2023

Aligned carbon fibers-carbon nanotube-polymer-based composite as lithium-ion battery current collector

High energy density demand is pushing the development of high-voltage cathode materials, which necessitates improved electrochemical stability of other battery components such as binders, electrolytes, and current collectors. Current collectors are considered to be an inactive component but still play an essential role. In this study, a metal-free composite film containing directionally aligned carbon fiber (CF), carbon nanotube (CNT), and polymer (P) was developed to replace aluminum foil as a cathode current collector, which relies on forming an Al 2 O 3 layer to ensure electrochemical stability at high voltage. Here, each component in the new cathode current collector played a functional role. The CNTs provided uniform current densities, and CFs improved the electronic conductivity and mechanical strength of the composite material. The polymer enhanced the adhesion of the cathode coating with the current collector and provided an impervious support to the cathode materials. The CF-CNT-P composite demonstrated excellent electrochemical and thermal stability. Cathodes coated on the CF-CNT-P composite exhibited lower charge transfer resistance, improved rate capability, and improved cyclic stability compared with the cathodes deposited on conventional aluminum foil. Additionally, the composite current collector was lighter (1.81 mg/cm 2 and 15 µm thick) than the commonly used aluminum foil (4.35 mg/cm2 and 15 µm thick), which can increase the cell energy density. Additionally, the CF-CNT-P did not need to be separated from the cathode coating during recycling and can be burnt out with binder, simplifying the recycling process.

25 ENERGY STORAGE↗

DOE OSTI2020

Significance of a Solid Electrolyte Interphase on Separation of Anode and Cathode Materials from Spent Li-Ion Batteries by Froth Flotation

The separation of electrode active materials from spent Li-ion batteries (LIBs) by froth flotation is challenging due to the changes in surface properties of electrode active materials from cycling as well as the presence of organic binders. In this work, the froth flotation separation of aged anode and cathode composite materials from spent LIBs was systematically investigated after the materials were heat treated. The results show that aged anode and cathode materials from spent LIBs can be well separated from each other after a heating process in air at 400 degrees C and at which some of the PVDF binder remains intact. The underlying mechanism was investigated by X-ray photoelectron spectroscopy (XPS), contact angle measurements, and scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX). The results from the XPS and contact angle measurements show that there is a hydrophilic and oxygen-rich layer on the surface of aged anode materials. This hydrophilic surface, associated with the solid electrolyte interface (SEI) layer, impacts the froth flotation process significantly. The results also show that both the SEI layers and PVDF binder residues on the surface are removed at 400 degrees C for an hour, restoring the hydrophobicity of the anode materials, which, in turn, benefits the separation of anode and cathode materials. The STEM/EDX elemental analysis data confirms that there are 20 nm-thick oxygen-rich SEI layers on the surfaces, which can be removed after a heating process. The present result illustrates the significance of the SEI layers in flotation separation of electrode materials and sheds new lights into the future development of the recycling processes for the separation of anode and cathode composite materials from spent Li-ion batteries.

25 ENERGY STORAGE↗

DOE OSTI2021

Investigation of Membrane Chemical Degradation as a Function of Catalyst Platinum Loading

Membrane chemical degradation is one of many factors that can impact fuel cell durability. Additionally, the fuel cell’s lifetime heavily depends on the membrane and its ability to maintain chemical and mechanical integrity. Previous studies indicate that chemical degradation is due to the formation of hydroxyl radicals that attack the polymer structure resulting in membrane thinning, pinhole formation, and the release of fluoride and sulfate ions. Membrane durability was investigated using ultra-low Pt electrode loadings (≤ 0.1 mg Pt cm -2 ). Accelerated stress testing (US-DOE protocols) demonstrated that the degradation rate was found to increase with higher Pt loadings. This is most likely due to more heterogeneous sites for radical formation due to hydrogen crossover to the cathode. We also explored membrane degradation rates while varying catalyst layer thickness, ionomer to carbon ratio, and types of carbon support. All of the aforementioned variables impact the membrane degradation rates.

25 ENERGY STORAGE↗

DOE OSTI2021

Predicting Pit Stability On Additively Manufactured SS316 Via Finite Element Modeling [Slides]

Pit growth and repassivation are complex, with many interconnecting geometric and environmental parameters to consider. Experimentally, it is difficult to isolate these individual parameters to study their effect on the stability of pits. To enable these studies, a finite element modeling approach has been developed to allow systematic testing of parameters that impact a pit’s stability. The specific parameters studied were the cathode diameter, the pit diameter and shape, and the water layer thickness. Hemispherical and rectangular-based pits were studied to determine the impact of the overall pit shape. Pit stability results were compared with mathematical calculations based on the Maximum Pit Model, for both 50% saturation and 100% saturated salt film coverage. Further studies expanded the range of pit geometry to those relevant to additively manufactured surfaces.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Ultra-fast and Thick Boriding of Geothermal Casing to Enhance Reliability

Harnessing the heat that is continuously generated underneath the Earth’s crust (geothermal) is a clean and renewable source of energy. Geothermal energy can be used to heat and cool buildings, including greenhouses, and to generate electrical power. Compared to other renewable energy sources such as solar and wind, geothermal energy is more reliable because it is available all the time and versatile in its many forms of application and deployment. Nonetheless, the deployment and extensive use of geothermal energy still lags behind other renewable sources due to some technical, but mainly economic challenges. Upfront costs of geothermal power well development are relatively high. Some of this high cost is attributed to the use of expensive construction materials to ensure adequate performance during operation. For example, Inconel 625, super duplex 2507, and titanium alloy materials are used in downhole casings, piping, and other components exposed to brine solution to withstand harsh operating environments (high temperature and corrosive environments). Relatively low-cost carbon steel can be used in many of these components in geothermal power plants; however, they are susceptible to excessive corrosion, thereby limiting their useful lifespan. Ultra-fast boriding (UFB) surface treatment of carbon steel may drastically increase its corrosion resistance thereby providing a cost-effective material solution in geothermal applications. Scientists at Argonne National Laboratory (ANL) recently developed a technique to accelerate the boriding process using a high-temperature electrochemical process to produce relatively thick boride layers on various metal and alloy materials in minutes rather than the several hours it takes through the typical pack boriding process; hence, the process is designated UFB. The process uses molten borax salt at 900– 1000°C in an electrochemical cell in which the material to be borided is the cathode and a graphite plate is the anode. Continuous and durable boride layers with thicknesses of 100–300 µm have been produced on a variety of metals and alloys in one hour. Such a surface layer can indeed be a cost-effective pathway to prevent corrosion of casing materials in contact with the chemically aggressive and corrosive geothermal brine fluids.

15 GEOTHERMAL ENERGY↗