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All sources NASA NTRS DOE OSTI

DOE OSTI2016

TH-CD-207B-01: BEST IN PHYSICS (IMAGING): Development of High Brightness Multiple-Pixel X-Ray Source Using Oxide Coated Cathodes

Purpose: To develop and characterize a high brightness multiple-pixel thermionic emission x-ray (MPTEX) source. Methods: Multiple-pixel x-ray sources allow for designs of novel x-ray imaging techniques, such as fixed gantry CT, digital tomosynthesis, tetrahedron beam computed tomography, etc. We are developing a high-brightness multiple-pixel thermionic emission x-ray (MPTEX) source based on oxide coated cathodes. Oxide cathode is chosen as the electron source due to its high emission current density and low operating temperature. A MPTEX prototype has been developed which may contain up to 41 micro-rectangular oxide cathodes in 4 mm pixel spacing. Electronics hardware was developed for source control and switching. The cathode emission current was evaluated and x-ray measurements were performed to estimate the focal spot size. Results: The oxide cathodes were able to produce ∼110 mA cathode current in pulse mode which corresponds to an emission current density of 0.55 A/cm{sup 2}. The maximum kVp of the MPTEX prototype currently is limited to 100 kV due to the rating of high voltage feedthrough. Preliminary x-ray measurements estimated the focal spot size as 1.5 × 1.3 mm{sup 2}. Conclusion: A MPTEX source was developed with thermionic oxide coated cathodes and preliminary source characterization was successfully performed. The MPTEX source is able to produce an array of high brightness x-ray beams with a fast switching speed.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2024

Solvent-mediated oxide hydrogenation in layered cathodes

Self-discharge and chemically induced mechanical effects degrade calendar and cycle life in intercalation-based electrochromic and electrochemical energy storage devices. In rechargeable lithium-ion batteries, self-discharge in cathodes causes voltage and capacity loss over time. The prevailing self-discharge model centers on the diffusion of lithium ions from the electrolyte into the cathode. Here, we demonstrate an alternative pathway, where hydrogenation of layered transition metal oxide cathodes induces self-discharge through hydrogen transfer from carbonate solvents to delithiated oxides. In self-discharged cathodes, we further observe opposing proton and lithium ion concentration gradients, which contribute to chemical and structural heterogeneities within delithiated cathodes, accelerating degradation. Hydrogenation occurring in delithiated cathodes may affect the chemo-mechanical coupling of layered cathodes as well as the calendar life of lithium-ion batteries.

25 ENERGY STORAGE↗

DOE OSTI2023

Understanding High-Voltage Behavior of Sodium-Ion Battery Cathode Materials Using Synchrotron X-ray and Neutron Techniques: A Review

Despite substantial research efforts in developing high-voltage sodium-ion batteries (SIBs) as high-energy-density alternatives to complement lithium-ion-based energy storage technologies, the lifetime of high-voltage SIBs is still associated with many fundamental scientific questions. In particular, the structure phase transition, oxygen loss, and cathode–electrolyte interphase (CEI) decay are intensely discussed in the field. Synchrotron X-ray and neutron scattering characterization techniques offer unique capabilities for investigating the complex structure and dynamics of high-voltage cathode behavior. In this review, to accelerate the development of stable high-voltage SIBs, we provide a comprehensive and thorough overview of the use of synchrotron X-ray and neutron scattering in studying SIB cathode materials with an emphasis on high-voltage layered transition metal oxide cathodes. We then discuss these characterizations in relation to polyanion-type cathodes, Prussian blue analogues, and organic cathode materials. Finally, future directions of these techniques in high-voltage SIB research are proposed, including CEI studies for polyanion-type cathodes and the extension of neutron scattering techniques, as well as the integration of morphology and phase characterizations.

25 ENERGY STORAGE↗

NASA NTRS2003

Plasma generation near an Ion thruster disharge chamber hollow cathode

In gridded electrostatic thrusters, ions are produced by electron bombardment in the discharge chamber. In most of these thrusters, a single, centrally located hollow cathode supplies the ionizing electrons. An applied magnetic field in the discharge chamber restricts the electrons leaving the hollow cathode to a very narrow channel. In this channel, the high electron current density ionizes both propellant gas flowing from the hollow cathode, and other neutrals from the main propellant flow from the plenum. The processes that occur just past the hollow cathode exit are very important. In recent engine tests, several cases of discharge cathode orifice place and keeper erosion have been reported. In this paper we present results from a new 1-D, variable area model of the plasma processes in the magnetized channel just downstream of the hollow cathode keeper. The model predicts plasma densities, and temperatures consistent with those reported in the literature for the NSTAR engine, and preliminary results from the model show a potential maximum just downstream of the cathode.

cathode↗

NASA NTRS2004

Hollow Cathode and Keeper-region Plasma Measurements Using Ultra-fast Miniature Scanning Probes

In order to support the development of comprehensive performance and life models for future deep space missions that will utilize ion thrusters, we have undertaken a study of the plasma structure in hollow cathodes using an new pneumatic scanning probe diagnostic. This device is designed to insert a miniature probe directly into the hollow cathode orifice from either the upstream insert region in the interior of the hollow cathode, or from the downstream keeper-plasma region at the exit of the hollow cathode, to provide complete axial profiles of the discharge plasma parameters. Previous attempts to diagnose this region with probes was Limited by the melting of small probes in the intense discharge near the orifice, or caused significant perturbation of the plasma by probes large enough to survive. Our new probe is extremely compact, and when configured as a single Langmuir probe, the ceramic tube insulator is only 0.5mm in diameter and the current collecting conductor has a total area of 0.002 cm2. A series of current-voltage characteristics are obtained by applying a rapid sawtooth voltage waveform to the probe as it is scanned by the pneumatic actuator into and out of the plasma region, The bellow-sealed pneumatic drive scans the probe 4 cm in the cathode insert region and 10 cm in the anode/keeper plasmas region at average speeds of about 1 mm/msec, and the residence time at the end of the insertion stroke in the densest part of the plasma near the orifice is measured to be only 10 msec. Since the voltage sweep time is fast compared to the motion of the probe, axial profiles of the plasma density, temperature and potential with reasonable spatial resolution are obtained. Measurements of the internal cathode pressures and the axial plasma-parameter profiles for a hollow cathode operating at discharge currents of up to 35 A in xenon will be presented.

plasma generation↗

NASA NTRS2004

Temperature Distributions in Hollow Cathode Emitters

Life-limiting processes in hollow cathodes are determined largely by the temperature of the emitter. To support development of cathode life models we have developed a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used determine the axial temperature profile. Thermocouples on the orifice plate provide measurements ofthe external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. Initial measurements of the temperature distribution in a hollow cathode with the same geometry as a cathode that failed after operating at 12 A emission current for 27800 hours are discussed.

ratio pyrometer system↗

DOE OSTI2017

DEGRADATION IN PERFORMANCE OF LANTHANUM STRONTIUM MANGANITE BASED SOLID OXIDE FUEL CELL CATHODES UNDER ACCELERATED TESTING

The performance of solid oxide fuel cells (SOFCs) with three different lanthanum strontium manganite (LSM) based cathode compositions were evaluated. All cells were yttria-stabilized zirconia (Zr0.92Y0.08O2-δ, 8YSZ) electrolyte-supported button cells, consisting of a nickel oxide – yttria-stabilized zirconia (NiO-8YSZ) anode and a cathode of 8YSZ and LSM. The three LSM compositions differed in the amount of excess Mn: Composition A was (La0.85Sr0.15)0.90MnO3±δ (10% excess Mn); Composition B was (La0.80Sr0.20)0.95MnO3±δ (5% excess Mn); and Composition C was (La0.80Sr0.20)0.98MnO3±δ (2% excess Mn). The cells were tested under conventional and accelerated conditions, where the accelerated conditions were meant to simulate the results of months of long-term testing in just 500 hours (approximately three weeks) of testing by using high operating temperature and current density. Accelerated tests showed lower degradation rates, lower continuous area specific resistance (ASR), and higher power output than conventional tests for all cathode compositions. Continuous measurements of the cells' output voltage versus time, together with periodic electrochemical impedance spectroscopy (EIS) measurements, were used to evaluate the performance of the cells in terms of ASR degradation rates (% ASR rise per kh) and power outputs. The EIS measurements also permitted a partial deconvolution of the cathode ASR from the anode ASR. Cathodes with 10% excess Mn tested under accelerated conditions had the lowest degradation rates, but the highest continuous ASR and lowest power outputs. Cathodes with 2% excess Mn tested under accelerated conditions had the lowest continuous ASR and highest power outputs; thus it was concluded that cells with the lowest amount of excess Mn cathodes performed the best.

08 HYDROGEN↗

DOE OSTI2021

Mixed Cationic and Anionic Redox in Ni and Co Free Chalcogen-Based Cathode Chemistry for Li-Ion Batteries

Mixed cationic and anionic redox cathode chemistry is emerging as conventional cationic-redox of transition metal based layered oxides are reaching their theoretical capacity limit. However, these anionic redox in transition metal oxide-based cathodes attained by taking excess lithium has resulted in stability issues due to weak metal - oxygen ligand covalency. Here, we present an alternative approach of improving metal - ligand covalency by introducing less electronegative chalcogen ligand (sulfur) in the cathode structural framework where the metal dband penetration into ligand p-band thereby utilizing reversible mixed anionic and cationic redox chemistry. Through this design strategy, we report possibility of developing a new family of layered cathode materials when partially filled d orbital redox couples like Fe 2+/3+ are introduced in the Li-ion conducting phase (Li 2 SnS 3 ). Further, the electron energy loss spectroscopy (EELS) and X-ray absorption near-edge structure (XANES) analysis are used to qualitatively identify the charge contributors at the metal and ligand sites during Li + extraction. The detailed high-resolution transmission electron microscopy (HR-TEM) and high annular dark field-scanning transmission electron microscopy (HAADF-STEM) investigation reveal the multi redox induced structural modifications and its surface amorphization with nanopore formation during cycling. Findings from this study will shed light on designing Ni and Co free chalcogen cathodes and various functional materials in the chalcogen based dual anionic and cationic redox cathode avenue.

25 ENERGY STORAGE↗

DOE OSTI2024

Electrolytic recovery of metals from lithium battery cathodes in moisture-tolerant molten hydroxide salt

Lithium-ion battery recycling offers an opportunity to develop innovative technologies to close the loop on the battery materials cycle and increase the resilience of the battery supply chain. Here, in this study, we demonstrate a two-step pyroelectrochemical method for producing mixed-metals from lithium-ion cathodes in a molten hydroxide salt. Mixed metal oxides in the form of insoluble lithium-ion cathode materials of LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) and spent lithium-ion battery materials (black mass) were electrochemically reduced to a soluble form and dissolved into a molten hydroxide salt bath. Electrochemical characterization of the process salt indicated accumulation of dissolved transition metals in the salt. A separate cathode was used to produce alloys of Ni, Mn, and Co electrochemically from the dissolved lithium-ion cathode materials. Characterization by scanning electron microscopy fitted with an energy dispersive X-ray spectrometer showed transition metals present in the cathode materials were recovered at the separate cathode. This approach represents a scalable, low temperature pyroelectrochemical process that can potentially reduce the cost and close the loop of battery cathode recycling.

25 ENERGY STORAGE↗

DOE OSTI2017

A new anion receptor for improving the interface between lithium- and manganese-rich layered oxide cathode and the electrolyte

Surface degradation on cycled lithium-ion battery cathode particles is governed not only by intrinsic thermodynamic properties of the material but also, oftentimes more predominantly, by the side reactions with the electrolytic solution. A superior electrolyte inhibits these undesired side reactions on the cathode and at the electrolyte interface, which consequently minimizes the deterioration of the cathode surface. The present study investigates a new boron-based anion receptor, tris(2,2,2-trifluoroethyl)borate (TTFEB), as an electrolyte additive in cells containing a lithium- and manganese-rich layered oxide cathode, Li 1.16 Ni 0.2 Co 0.1 Mn 0.54 O 2 . Our electrochemical studies demonstrate that the cycling performance and Coulombic efficiency are significantly improved because of the additive, in particular, under elevated temperature conditions. Spectroscopic analyses revealed that the addition of 0.5 wt % TTFEB is capable of reducing the content of lithium-containing inorganic species within the cathode-electrolyte interphase layer and minimizing the reduction of tetravalent Mn4+ at the cathode surface. Furthermore, our work introduces a novel additive highly effective in improving lithium-ion battery performance, highlights the importance in preserving the surface properties of cathode materials, and provides new insights on the working mechanism of electrolyte additives.

25 ENERGY STORAGE↗

DOE OSTI2022

Review of Multifunctional Separators: Stabilizing the Cathode and the Anode for Alkali (Li, Na, and K) Metal–Sulfur and Selenium Batteries

Alkali metal batteries based on lithium, sodium, and potassium anodes and sulfur-based cathodes are regarded as key for next-generation energy storage due to their high theoretical energy and potential cost effectiveness. However, metal–sulfur batteries remain challenged by several factors, including polysulfides’ (PSs) dissolution, sluggish sulfur redox kinetics at the cathode, and metallic dendrite growth at the anode. Functional separators and interlayers are an innovative approach to remedying these drawbacks. Here we critically review the state-of-the-art in separators/interlayers for cathode and anode protection, covering the Li–S and the emerging Na–S and K–S systems. The approaches for improving electrochemical performance may be categorized as one or a combination of the following: Immobilization of polysulfides (cathode); catalyzing sulfur redox kinetics (cathode); introduction of protective layers to serve as an artificial solid electrolyte interphase (SEI) (anode); and combined improvement in electrolyte wetting and homogenization of ion flux (anode and cathode). It is demonstrated that while the advances in Li–S are relatively mature, less progress has been made with Na–S and K–S due to the more challenging redox chemistry at the cathode and increased electrochemical instability at the anode. Throughout these sections there is a complementary discussion of functional separators for emerging alkali metal systems based on metal–selenium and the metal–selenium sulfide. The focus then shifts to interlayers and artificial SEI/cathode electrolyte interphase (CEI) layers employed to stabilize solid-state electrolytes (SSEs) in metal–sulfur solid-state batteries (SSBs). The discussion of SSEs focuses on inorganic electrolytes based on Li- and Na-based oxides and sulfides but also touches on some hybrid systems with an inorganic matrix and a minority polymer phase. The review then moves to practical considerations for functional separators, including scaleup issues and Li–S technoeconomics. The review concludes with an outlook section, where we discuss emerging mechanics, spectroscopy, and advanced electron microscopy (e.g. cryo-transmission electron microscopy (cryo-TEM) and cryo-focused ion beam (cryo-FIB))-based approaches for analysis of functional separator structure–battery electrochemical performance interrelations. Finally, throughout the review we identify the outstanding open scientific and technological questions while providing recommendations for future research topics.

25 ENERGY STORAGE↗

DOE OSTI2020

Probing Thermal Stability of Li-Ion Battery Ni-Rich Layered Oxide Cathodes by means of Operando Gas Analysis and Neutron Diffraction

Thermal stability is a crucial parameter that must be considered within the overall performance metrics of Ni-rich layered oxide cathodes. While the intrinsic structural stability of the cathode materials under thermal conditions is important, it is also critical to consider their reaction with electrolytes. In this study, operando gas analysis, ex situ neutron diffraction, and differential scanning calorimetry were combined to give a broader picture of the thermal stability of Ni-rich NMC cathodes. Li 1– x Ni 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) composite materials with four different states of charge were investigated with and without the presence of an electrolyte. It has been found that electrolyte can greatly accelerate both the structural and thermal decomposition of the cathode materials. A higher state of charge will also make cathode materials more susceptible to thermal shock. Without an electrolyte, O 2 release inducing a structural change from layered to rock salt was the major observation during thermal runaway. However, all samples retained some levels of layered structure after annealing up to 300 °C without the electrolyte. In comparison, almost all the O3-type layered phase transformed to the rock-salt phase for the cathode materials heated with the electrolyte at the same experimental conditions. Moreover, the amount of CO 2 increased by nearly two orders of magnitude when annealing cathode materials with electrolyte in operando gas analysis experiments. More delithiated NMC811 samples released larger amounts of CO 2 at earlier onset temperatures, resonating well with the differential scanning calorimetry (DSC) results showing that more delithiated samples release more heat during thermal shock.

25 ENERGY STORAGE↗

DOE OSTI2025

Anion Exchange Membrane Water Electrolysis Using a Catalyst-Coated Membrane Cathode

A catalyst-coated membrane (CCM) approach to electrode fabrication for high pH water electrolysis offers enhanced interfacial contact between the catalyst layer and the membrane surface in comparison to the catalyst-coated substrate (CCS) electrode configuration. The CCM facilitates enhanced ionic and water transport between the cathode and the anion exchange membrane (AEM). This advantage is particularly significant with AEM water electrolysis (compared to proton exchange membrane water electrolysis) because the cathode typically operates under dry conditions and relies solely on diffusive water transport across the AEM from the liquid-fed anode. This study presents a direct performance comparison between CCS and CCM cathode configurations using identical hydrogen evolution reaction (HER) catalysts and other components. The use of a pseudo-reference electrode integrated into the membrane electrode assembly enabled detailed analysis of the CCM cathode polarization behavior. Surface characterization provided insight into the degradation mechanisms associated with the CCM configuration. Optimization of the cathode ionomer cross-link density improved both the cathode polarization performance and the electrolysis device durability. Further optimization of the HER catalyst loading in the CCM cathode resulted in additional gains in the electrolysis efficiency. Collectively, these findings offer valuable guidance for the design and fabrication of high-performance, durable AEM electrolysis CCMs.

Water electrolysis↗

DOE OSTI2018

Detrimental Effects of Chemical Crossover from the Lithium Anode to Cathode in Rechargeable Lithium Metal Batteries

The interfacial stability is one of the crucial factors affecting long-term cyclability of lithium (Li) metal batteries (LMBs). While cross contamination (such as Mn+2 crossover from cathode to contaminate graphite anode) phenomena has been well studied in Li ion batteries (LIBs), the similar phenomena has rarely been studied in LMBs. Here, we systematically investigated the cathode failure triggered by the chemical crossover between the electrode pair in rechargeable LMBs. In strong contrast to LIBs, the cathode in LMBs suffers more significant and irreversible capacity fade during cycling and its capacity cannot be fully recovered even when Li metal anode has been replaced in the successive cycling. In-depth characterizations of the cathode surface reveal severe CEI deterioration related to the accumulation of highly resistive polymeric components and lithium fluoride. The soluble decomposition products generated by extensive salt-anion decomposition at Li metal surface can diffuse toward cathode side and result in severe deterioration of cathode as well asseparator surfaces. A polydopamine coated separator with selective Li-ion permeability has been developed to mitigate the detrimental chemical crossover and enhance the cathode stability.

Lee, Hongkyung↗

DOE OSTI2024

Electrochemical reactivity and passivation of organic electrolytes at spinel MgCrMnO 4 cathode interfaces for rechargeable high voltage magnesium-ion batteries

Magnesium transition metal oxides such as MgCr 2−x Mn x O 4 are promising high-voltage and high-capacity cathode materials for rechargeable magnesium batteries (RMBs). Understanding and improving the chemical and electrochemical stability of the cathode–electrolyte interface (CEI) has been the primary technical emphasis to enable this category of cathode materials, which has been significantly underexplored. Herein, in this study, we focus on investigating the fundamental mechanism of parasitic reactions at the charged surface of the high-voltage MgCrMnO 4 model cathode with different organic electrolytes. The aim is to reveal the underlying effect of anions and solvents responsible for the passivation behavior of the cathode by using three exemplary anions: [(CF 3 SO 2 ) 2 N] − (TFSI − ), Al[OC(CF 3 ) 3 ] 4 − (TPFA − ), and [CB 11 H 12 ] − (MC) and three solvents: diglyme (G2), triglyme (G3), and 3-methoxypropylamine (MPA). High precision leakage current measurements during potentiostatic hold reveal that the electrolyte solvent chemistry has a more profound impact than anion's on the passivation of the MgCrMnO 4 cathode surface during deintercalation of Mg 2+ . X-ray photoelectron spectroscopy exhibits the differences in CEI composition. Amine solvents like MPA show poor passivation due to a higher degree of solvent decomposition, while the thin and anion-derived CEI in glyme-based electrolytes is directly linked with the better passivation behavior on the cathode. Furthermore, we leverage the knowledge from these findings to modify the electrolyte structure by adding a solvent additive, with the goal of reducing the parasitic reaction.

25 ENERGY STORAGE↗

DOE OSTI2026

Fe-single atom catalysts facilitate fast electron transfer with MoS 2 /SnS 2 cathodes in lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) emerge as promising next-generation energy storage systems offering cost-effectiveness, environmental friendliness, and high theoretical energy density. The practical implementation of LSBs faces significant hindrances due to the shuttle effect and sluggish redox reactions. To address these challenges, single-atom catalyst (SAC) based combination materials from d-block elements can offer increased active catalytic sites, rapid charge transfer, accelerated electron migration, and fast sulfur redox conversion kinetics of lithium polysulfides (LiPSs). In this study, we fabricated three different LSB cathodes: pure S, S@MoS 2 /SnS 2 , and S@Fe–MoS 2 /SnS 2 . These cathodes were then used to explore the cycle life, capacity, rate capability, and redox kinetic reactions of LiPSs while assessing the influence of Fe-SACs on their performance. As a result, LSBs with S@Fe–MoS 2 /SnS 2 cathodes demonstrate an extended cycle life of 1000 cycles at a C-rate of 0.2C, maintaining a capacity close to 500 mA h g −1 , the highest initial discharge capacity of 1622 mA h g −1 and 1066 mA h g −1 at 0.05C and 0.2C, and excellent rate capabilities of 708 mA h g −1 and 558 mA h g −1 at 1C and 2C, respectively. The synergistic effect of the Fe-SAC-based combination cathode (S@Fe–MoS 2 /SnS 2 ) creates plentiful adsorptive and highly active catalytic sites, resulting in substantially enhanced capacity for adsorbing soluble long-chain LiPSs. This facilitates ultra-fast redox kinetics, surpassing the performance of the S@MoS 2 /SnS 2 and pure S cathodes. In the ex situ analysis, results from powder X-ray diffraction (XRD) to observe the new phase, soft X-ray absorption spectroscopy (XAS) to investigate the electronic structure, and hard X-ray photoelectron microscopy (HAXPES) with different energies (900 eV, 2000 eV, and 6000 eV) to track the chemical-state evolution of Fe-SACs in MoS 2 /SnS 2 cathodes displayed notable electrochemical reversibility involving S 8 ⇄ LiPSs ⇄ Li 2 S conversion even after 1000 cycles. Additionally, in situ, operando Raman analysis can unveil a novel catalytic mechanism of Fe-SACs in MoS 2 /SnS 2 “facilitating rapid electron transfer” during the discharge and charge processes of LSBs involving the conversion of S 8 ⇄ long-chain LiPSs ⇄ Li 2 S 2 /Li 2 S. This study elucidates the working mechanism of Fe-SAC cathodes, offering insights into overcoming the shuttle effect and facilitating sulfur redox kinetics to advance commercial LSBs.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Deciphering the Conflict Between Ion and Electron Percolating Networks in Solid-State Battery Cathodes

High-energy- and power-density solid state batteries require an optimal cathode composition and microstructural arrangement of cathode active material, solid-state electrolyte, conductive carbon, and binder to simultaneously support lithium-ion transport, electron conduction, and storage capacity. The ion and electron conducting phases in solid-state cathodes counteract each other's percolating networks as their mass ratios increase or decrease relative to each other. Here, we investigate targeted mass ratio variations of argyrodite solid electrolyte and two different types of conductive carbon (particles and fibers) in composite LiNi0.8Mn0.1Co0.1O2 (NMC811) solid-state cathodes to ascertain the ionic-electronic tradeoffs in cathode performance. Through ionic and electronic conductivity measurements on composite cathodes, as well as rate-testing and cycling performance in full cells, it is shown that the conductive carbon fibers form a percolative electronic network within the composite at a lower mass ratio (3-5 wt%) than particulate carbon (>5 wt%). The threshold to achieve electronic percolation coincides with higher accessible capacity in the cathode as the active material particles become electronically connected. However, carbon loadings beyond this percolation threshold lead to increased ion transport resistance, arising from disruptions to ionic conduction pathways and degraded contact at the interface between the electrolyte and active materials. Imaging, spectroscopy, and physics-based models quantitatively describe the relationship between carbon and electrolyte compositions and the cell's capacity and rate performance through percolation theory. This work demonstrates the importance of quantitatively understanding percolating networks in solid-state cells and that strategic engineering of conductive carbon morphologies can further increase the energy- and power-density of solid-state cells.

25 ENERGY STORAGE↗

DOE OSTI2019

Topological cathodes: Controlling the space charge limit of electron emission using metamaterials

The space charge limit (SCL) of emission from photocathodes sets an upper limit on the performance of both high- and low-field electron guns. Generally, one is forced to strike a compromise between the space charge limit and the cathode’s intrinsic emittance [I. Bazarov et al., Phys. Rev. Lett. 102, 104801 (2009)]. However, it is possible to nearly eliminate the SCL due to the image charge by engineering the topography of the cathode’s surface. A cathode with a surface plasma frequency below the frequency spectrum of the accelerating electrons will greatly reduce the polarization of the cathode and its image-charge field, thereby mitigating the cathode’s space charge limit for photoelectric, thermionic, and field emission. In the work presented here, a theory for the image-charge field of a disk of charge being accelerated from the cathode surface is developed which includes the frequency-dependent effects of the cathode’s dielectric function. This theory verifies the concept of SCL mitigation with a wire array metamaterial to design a metacathode with greatly reduced image-charge fields. The details of the holistic metacathode design spanning 6 orders of magnitude in scale are described.

47 OTHER INSTRUMENTATION↗