Search NASA⌕ Search

SEARCH · Search NASA

Results for “anionic oxygen redox”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

An Investigation of the Electrochemical Activity of (Ba/Sr)FeO 3-y Anodes

FeO x , SrFeO 3-y (SF), and Ba 0.5 Sr 0.5 FeO 3–y (BSF) were studied for application as fuel oxidation catalysts in solid oxide fuel cells (SOFC) anodes. Electrodes were prepared by impregnation into porous yttria-stabilized zirconia (YSZ), with La 0.3 Sr 0.7 TiO 3–y (LST) added for electronic conductivity. The electrode impedances decreased dramatically upon addition of SF and BSF and much less when only SrO or FeO x were added. Temperature Programmed Desorption (TPD) of O 2 from oxidized BSF showed O 2 desorbing between 200 °C and 700 °C, while no O 2 desorbed from Fe 2 O 3 below 900 °C. The results, together with thermodynamic analysis, suggest that stabilization of Fe +4 in the perovskite lattice plays an important role in enhancing the catalytic activity of SF and BSF by providing access to a Fe 3+ /Fe 4+ redox couple that can accept oxygen anions from the yttria-stabilized zirconia (YSZ) electrolyte. Oxygen is weakly bound to these sites facilitating its reaction with adsorbed H 2 .

Electrochemistry↗
DOE OSTI2020

Role of Redox-Inactive Transition-Metals in the Behavior of Cation-Disordered Rocksalt Cathodes

Owing to the capacity boost from oxygen redox activities, Li-rich cation-disordered rocksalts (LRCDRS) represent a new class of promising high-energy Li-ion battery cathode materials. Redox-inactive transition-metal (TM) cations, typically d 0 TM, are essential in the formation of rocksalt phases, however, their role in electrochemical performance and cathode stability is largely unknown. In the present study, the effect of two d 0 TM (Nb 5+ and Ti 4+ ) is systematically compared on the redox chemistry of Mn-based model LRCDRS cathodes, namely Li 1.3 Nb 0.3 Mn 0.4 O 2 (LNMO), Li 1.25 Nb 0.15 Ti 0.2 Mn 0.4 O 2 (LNTMO), and Li 1.2 Ti 0.4 Mn 0.4 O 2 (LTMO). Although electrochemically inactive, d 0 TM serves as a modulator for oxygen redox, with Nb 5+ significantly enhancing initial charge storage contribution from oxygen redox. Further studies using differential electrochemical mass spectroscopy and resonant inelastic X-ray scattering reveal that Ti 4+ is better in stabilizing the oxidized oxygen anions (O n- , 0 < n < 2), leading to a more reversible O redox process with less oxygen gas release. As a result, much improved chemical, structural and cycling stabilities are achieved on LTMO. Detailed evaluation on the effect of d 0 TM on degradation mechanism further suggests that proper design of redox-inactive TM cations provides an important avenue to balanced capacity and stability in this newer class of cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

Stabilized Co-Free Li-Rich Oxide Cathode Particles with An Artificial Surface Prereconstruction

Li-rich metal oxide (LXMO) cathodes have attracted intense interest for rechargeable batteries because of their high capacity above 250 mAh g –1 . However, the side effects of hybrid anion and cation redox (HACR) reactions, such as oxygen release and phase collapse that result from global oxygen migration (GOM), have prohibited the commercialization of LXMO. GOM not only destabilizes the oxygen sublattice in cycling, aggravating the well-known voltage fading, but also intensifies electrolyte decomposition and Mn dissolution, causing severe full-cell performance degradation. In this study, an artificial surface prereconstruction (ASR) for Li 1.2 Mn 0.6 Ni 0.2 O 2 particles with a molten-molybdate leaching is conducted, which creates a crystal-dense anion-redox-free LiMn 1.5 Ni 0.5 O 4 shell that completely encloses the LXMO lattice (ASR-LXMO). Differential electrochemical mass spectroscopy and soft X-ray absorption spectroscopy analyses demonstrate that GOM is shut down in cycling, which not only stabilizes HACR in ASR-LXMO, but also mitigates the electrolyte decomposition and Mn dissolution. ASR-LXMO displays greatly stabilized cycling performance as it retains 237.4 mAh g –1 with an average discharge voltage of 3.30 V after 200 cycles. More crucially, while the pristine LXMO cycling cannot survive 90 cycles in a pouch full-cell matched with a commercial graphite anode and lean (2 g A –1 h –1 ) electrolyte, ASR-LXMO shows high capacity retention of 76% after 125 cycles in full-cell cycling.

25 ENERGY STORAGE↗
DOE OSTI2022

Unveiling the High-valence Oxygen Degradation Across the Delithiated Cathode Surface

Charge compensation on anionic redox reaction (ARR) has been promising to realize extra capacity beyond transition metal redox in battery cathodes. The practical development of ARR capacity has been hindered by high-valence oxygen instability, particularly at cathode surfaces. However, the direct probe of surface oxygen behavior has been challenging. Here, the electronic states of surface oxygen are investigated by combining mapping of resonant Auger electronic spectroscopy (mRAS) and ambient pressure X-ray photoelectron spectroscopy (APXPS) on a model LiCoO 2 cathode. The mRAS verified that no high-valence oxygen can sustain at cathode surfaces, while APXPS proves that cathode electrolyte interphase (CEI) layer evolves and oxidizes upon oxygen gas contact. In conclusion, this work provides valuable insights into the high-valence oxygen degradation mode across the interface. Oxygen stabilization from surface architecture is proven a prerequisite to the practical development of ARR active cathodes.

25 ENERGY STORAGE↗
DOE OSTI2022

Exceptional Cycling Performance Enabled by Local Structural Rearrangements in Disordered Rocksalt Cathodes

The capacity of lithium transition-metal (TM) oxide cathodes is directly linked to the magnitude and accessibility of the redox reservoir associated with TM cations and/or oxygen anions, which traditionally decreases with cycling as a result of chemical, structural, or mechanical fatigue. Here, it is shown that a capacity increase over 125% can be achieved upon cycling of high-energy Mn- and F-rich cation-disordered rocksalt oxyfluoride cathodes. This study reveals that in Li 1.2 Mn 0.7 Nb 0.1 O 1.8 F 0.2 , repeated Li extraction/reinsertion utilizing Mn 3+ /Mn 4+ redox along with some degree of O-redox participation leads to local structural rearrangements and formation of domains with off-stoichiometry spinel-like features. The effective integration of these local “structure-domains” within the cubic disordered rocksalt framework promotes better Li diffusion and improves material utilization, consequently increased capacity upon cycling. Finally, this study provides important new insights into materials design strategies to further exploit the rich compositional and structural space of Mn chemistry for developing sustainable, high-energy cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2021

The Role of Metal Substitution in Tuning Anion Redox in Sodium Metal Layered Oxides Revealed by X‐Ray Spectroscopy and Theory

Abstract We investigate high‐valent oxygen redox in the positive Na‐ion electrode P2‐Na 0.67− x [Fe 0.5 Mn 0.5 ]O 2 (NMF) where Fe is partially substituted with Cu (P2‐Na 0.67− x [Mn 0.66 Fe 0.20 Cu 0.14 ]O 2 , NMFC) or Ni (P2‐Na 0.67− x [Mn 0.65 Fe 0.20 Ni 0.15 ]O 2 , NMFN). From combined analysis of resonant inelastic X‐ray scattering and X‐ray near‐edge structure with electrochemical voltage hysteresis and X‐ray pair distribution function profiles, we correlate structural disorder with high‐valent oxygen redox and its improvement by Ni or Cu substitution. Density of states calculations elaborate considerable anionic redox in NMF and NMFC without the widely accepted requirement of an A‐O‐A′ local configuration in the pristine materials (where A=Na and A′=Li, Mg, vacancy, etc.). We also show that the Jahn–Teller nature of Fe 4+ and the stabilization mechanism of anionic redox could determine the extent of structural disorder in the materials. These findings shed light on the design principles in TM and anion redox for positive electrodes to improve the performance of Na‐ion batteries.

Abate, Iwnetim↗
DOE OSTI2021

The Role of Metal Substitution in Tuning Anion Redox in Sodium Metal Layered Oxides Revealed by X-Ray Spectroscopy and Theory

We investigate high-valent oxygen redox in the positive Na-ion electrode P2-Na 0.67-x [Fe 0.5 Mn 0.5 ]O 2 (NMF) where Fe is partially substituted with Cu (P2-Na 0.67-x [Mn 0.66 Fe 0.20 Cu 0.14 ]O 2 , NMFC) or Ni (P2-Na 0.67 -x[Mn 0.65 Fe 0.20 Ni 0.15 ]O 2 , NMFN). From combined analysis of resonant inelastic X-ray scattering and X-ray near-edge structure with electrochemical voltage hysteresis and X-ray pair distribution function profiles, we correlate structural disorder with high-valent oxygen redox and its improvement by Ni or Cu substitution. Density of states calculations elaborate considerable anionic redox in NMF and NMFC without the widely accepted requirement of an A-O-A' local configuration in the pristine materials (where A=Na and A'=Li, Mg, vacancy, etc.). We also show that the Jahn–Teller nature of Fe 4+ and the stabilization mechanism of anionic redox could determine the extent of structural disorder in the materials. These findings shed light on the design principles in TM and anion redox for positive electrodes to improve the performance of Na-ion batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Coulombically-stabilized oxygen hole polarons enable fully reversible oxygen redox

Stabilizing high-valent redox couples and exotic electronic states necessitates an understanding of the stabilization mechanism. In oxides, whether they are being considered for energy storage or computing, highly oxidized oxide-anion species rehybridize to form short covalent bonds and are related to significant local structural distortions. In intercalation oxide electrodes for batteries, while such reorganization partially stabilizes oxygen redox, it also gives rise to substantial hysteresis. In this work, we investigate oxygen redox in layered Na 2-x Mn 3 O 7 , a positive electrode material with ordered Mn vacancies. We prove that coulombic interactions between oxidized oxide-anions and the interlayer Na vacancies can disfavor rehybridization and stabilize hole polarons on oxygen (O-) at 4.2 V vs. Na/Na + . These coulombic interactions provide thermodynamic energy saving as large as O–O covalent bonding and enable ~40 mV voltage hysteresis over multiple electrochemical cycles with negligible voltage fade. As such, our results establish a complete picture of redox energetics by highlighting the role of coulombic interactions across several atomic distances and suggest avenues to stabilize highly oxidized oxygen for applications in energy storage and beyond.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A Fluorination Method for Improving Cation-Disordered Rocksalt Cathode Performance

In Li-rich cation-disordered rocksalt oxide cathodes (DRX), partial fluorine substitution in the oxygen anion sublattice can increase the capacity contribution from transition-metal (TM) redox while reducing that from the less reversible oxygen redox. To date, limited fluorination substitution has been achieved by introducing LiF precursor during the solid-state synthesis. To take full advantage of the fluorination effect, however, a higher F content is desired. In the present study, the successful use of a fluorinated polymeric precursor is reported to increase the F solubility in DRX and the incorporation of F content up to 10–12.5 at% into the rocksalt lattice of a model Li-Mn-Nb-O (LMNO) system, largely exceeding the 7.5 at% limit achieved with LiF synthesis. Higher F content in the fluorinated-DRX (F-DRX) significantly improves electrochemical performance, with a reversible discharge capacity of ≈255 mAh g –1 achieved at 10 at% of F substitution. After 30 cycles, up to a 40% increase in capacity retention is achieved through the fluorination. Overall, the study demonstrates the feasibility of using a new and effective fluorination process to synthesize advanced DRX cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2025

Transition metal vacancy and position engineering enables reversible anionic redox reaction for sodium storage

Triggering the anionic redox reaction is an effective approach to boost the capacity of layered transition metal (TM) oxides. However, the irreversible oxygen release and structural deterioration at high voltage remain conundrums. Herein, a strategy for Mg ion and vacancy dual doping with partial TM ions pinned in the Na layers is developed to improve both the reversibility of anionic redox reaction and structural stability of layered oxides. Both the Mg ions and vacancies (□) are contained in the TM layers, while partial Mn ions (~1.1%) occupy the Na-sites. The introduced Mg ions combined with vacancies not only create abundant nonbonding O 2p orbitals in favor of high oxygen redox capacity, but also suppress the voltage decay originated from Na–O–□ configuration. The Mn ions pinned in the Na layers act as “rivets” to restrain the slab gliding at extreme de-sodiated state and thereby inhibit the generation of cracks. The positive electrode, Na 0.67 Mn 0.011 [Mg 0.1 □ 0.07 Mn 0.83 ]O 2 , delivers an enhanced discharge capacity and decent cyclability. This study provides insights into the construction of stable layered oxide positive electrode with highly reversible anionic redox reaction for sodium storage.

Cai, Congcong [Wuhan Univ. of Technology (China)]↗
DOE OSTI2021

Unlocking anionic redox activity in O3-type sodium 3 d layered oxides via Li substitution

Sodium ion batteries, because of their sustainability attributes, could be an attractive alternative to Li-ion technology for specific applications. However, it remains challenging to design high energy density and moisture stable Na-based positive electrodes. Here, we report an O3-type NaLi 1/3 Mn 2/3 O 2 phase showing anionic redox activity, obtained through a ceramic process by carefully adjusting synthesis conditions and stoichiometry. This phase shows a sustained reversible capacity of 190 mAh g -1 that is rooted in cumulative oxygen and manganese redox processes as deduced by combined spectroscopy techniques. Unlike many other anionic redox layered oxides so far reported, O3-NaLi 1/3 Mn 2/3 O 2 electrodes do not show discernible voltage fade on cycling. This finding, rationalized by density functional theory, sheds light on the role of inter- versus intralayer 3d cationic migration in ruling voltage fade in anionic redox electrodes. Another practical asset of this material stems from its moisture stability, hence facilitating its handling and electrode processing. Altogether, this work offers future directions towards designing highly performing sodium electrodes for advanced Na-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Correlating concerted cations with oxygen redox in rechargeable batteries

Rechargeable batteries currently power much of our world, but with the increased demand for electric vehicles (EVs) capable of traveling hundreds of miles on a single charge, new paradigms are necessary for overcoming the limits of energy density, particularly in rechargeable batteries. The emergence of reversible anionic redox reactions presents a promising direction toward achieving this goal; however this process has both positive and negative effects on battery performance. While it often leads to higher capacity, anionic redox also causes several unfavorable effects such as voltage fade, voltage hysteresis, sluggish kinetics, and oxygen loss. However, the introduction of cations with topological chemistry tendencies has created an efficient pathway for achieving long-term oxygen redox with improved kinetics. The cations serve as pillars in the crystal structure and meanwhile can interact with oxygen in ways that affect the oxygen redox process through their impact on the electronic structure. This review delves into a detailed examination of the fundamental physical and chemical characteristics of oxygen redox and elucidates the crucial role that cations play in this process at the atomic and electronic scales. Furthermore, here we present a systematic summary of polycationic systems, with an emphasis on their electrochemical performance, in order to provide perspectives on the development of next-generation cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

Fluorination effect for stabilizing cationic and anionic redox activities in cation-disordered cathode materials

We see that cation-disordered Li-excess cathodes with oxygen redox reactions are promising candidates for high-energy-density Li ion batteries. Nevertheless, the oxygen redox process that is required for the high capacity often comes with the oxygen loss, which leads to severe capacity degradation and voltage decay. In this work, we have successfully synthesized a series of Li-excess cation-disordered cathodes (Li 1.2 Mn 0.4+x Ti 0.4-x O 2-x Fx) (0 ≤ x ≤ 0.2) with different fluorine (F) contents. The electrochemical performance results show that the Li 1.2 Mn 0.55 Ti 0.25 O 1.85 F 0.15 (LMTOF0.15) exhibits the highest reversible capacity (275 mAh g -1 , under 30 mA g -1 ), cyclability, and voltage retentions. The mapping of resonant inelastic X-ray scattering (mRIXS) and differential electrochemical mass spectroscopy (DEMS) results reveal that the fluorination enhances the reversible lattice oxygen redox reaction while suppressing irreversible gas release and surface reactions. The X-ray Absorption Spectroscopy (XAS) during the initial two cycles shows that F-substitution alleviates the reduction of the Mn valence state during the whole (dis)charge processes in the bulk and at the surface of the material, results in higher average discharge voltage. In addition, the introduction of F improves the structural stability and suppresses local lattice distortion of the material. Therefore, LMTOF 0.15 is able to cycle with smaller polarization, less interfacial side reaction and Mn dissolution, and therefore results in enhanced cyclability. This work provides a comprehensive understanding of the fluorination effect on the cationic and anionic redox activities in cation-disordered Li-excess cathodes.

25 ENERGY STORAGE↗
DOE OSTI2022

Iron precipitation under controlled oxygen flow: Mineralogical implications for BIF precursors in the Archean ocean

Banded iron formation (BIF) deposition in the Archean ocean is thought to have been initiated by the oxidation of dissolved iron into ferric primary precursor phases that descended through the water column and were deposited on the seafloor. Effective interpretation of the trace element and isotopic composition of BIFs in the geologic record requires an understanding of the identity and longevity of those precursor phases. Temporal and spatial variation in oxidant concentration and ocean chemistry may have driven precursor mineralogy. Furthermore, precursor phases may undergo transitions during descent and burial. This experimental study follows the evolution of iron mineralogy, speciation, and redox state during the precipitation of iron under variable oxygen fluxes and in fluids containing different iron-complexing anions (chloride, sulfate, and phosphate). Additionally, suspensions collected after incomplete oxidation were anoxically aged to simulate changes to precursor mineralogy during descent below the seawater redoxcline. Results from X-ray diffraction, sequential dissolution, colorimetric determination of Fe redox state, and Fe K-edge X-ray absorption fine structure spectroscopy showed that under all experimental conditions, intermediate precipitates collected before complete iron uptake contained mineralized ferrous iron. Purely ferric mineral assemblages were not observed until iron was removed from solution. In low-oxygen experiments, intermediate precipitates contained phases with stoichiometric Fe 2+ , including magnetite, vivianite, and green rust (GR). Chloride green rust (GR1) had more ferric iron than sulfate green rust (GR2) and more readily transitioned to magnetite via disproportionation. GR2 was stable over a broader range of iron uptake; magnetite appeared mainly as an additional oxidation product in sulfate solution. In high oxygen experiments, mineralized ferrous iron occurred in amorphous phases or as a non-stoichiometric component in ferric oxides; final ferric assemblages were less crystalline than in low-oxygen equivalents. Low concentrations of phosphate increased the total iron oxidation rate, but also increased the ferrous content of intermediate precipitates. The incorporation of phosphate stabilized GR2 and facilitated GR2 precipitation over a larger range of iron uptake. In higher concentrations of phosphate, vivianite and poorly crystalline ferric hydroxides formed in place of GR. Here, these findings suggest that over a range of possible ocean chemistries, mixed-valence phases may have been short lived but relevant precursors to BIF. Additionally, anionic chemistry and oxidant concentration are shown to influence the crystallinity and chemical resistivity of final ferric assemblages, affecting their reactivity during later anoxic burial.

58 GEOSCIENCES↗
DOE OSTI2023

Designing High‐Donicity Anions for Rechargeable Potassium Superoxide/Peroxide Batteries

Abstract A battery cathode based on the superoxide/peroxide redox not only inherits the advantage of oxygen (O 2 ) batteries in high capacities and low costs but also overcomes the disadvantages in O 2 storage, electrolyte evaporation, and anode deactivation due to O 2 crossover. Herein, we report an enhanced potassium superoxide (KO 2 )/peroxide (K 2 O 2 ) conversion by adopting a high‐donicity anion additive in the ether‐based electrolyte. Such an anion was synthesized via a “Solvent‐in‐Anion” strategy and validated to enhance the electron donicity of the electrolyte. The use of high‐donicity anion could lead to enhanced KO 2 utilization (≈90.2 %) by retarding electrode passivation and allow the full charging back of K 2 O 2 through the solution‐mediated pathway without electrocatalysts. No apparent cell degradation is observed during the first 120 cycles by controlling the reversible depth‐of‐discharge capacity at 292 mAh g −1 within an O 2 ‐free region. The K−KO 2 cell delivers a high energy efficiency (>84.4 %) and a lifespan of over 1440 hours.

Qin, Lei↗
DOE OSTI2021

Thermally Aged Li–Mn–O Cathode with Stabilized Hybrid Cation and Anion Redox

Though low-cost and environmentally friendly, Li–Mn–O cathodes suffer from low energy density. Although synthesized Li 4 Mn 5 O 12 -like overlithiated spinel cathode with reversible hybrid anion- and cation-redox (HACR) activities has a high initial capacity, it degrades rapidly due to oxygen loss and side-reaction-induced electrolyte decomposition. In this study, we develop a two-step heat treatment to promote local decomposition as Li 4 Mn 5 O 12 → 2LiMn 2 O 4 + Li 2 MnO 3 + 1/2 O 2 ↑, which releases near-surface reactive oxygen that is harmful to cycling stability. The produced nanocomposite delivers a high discharge capacity of 225 mAh/g and energy density of over 700 Wh/kg at active-material level at a current density of 100 mA/g between 1.8 to 4.7 V. Benefiting from suppressed oxygen loss and side reactions, 80% capacity retention is achieved after 214 cycles in half cells. With industrially acceptable electrolyte amount (6 g/Ah), full cells paired with Li 4 Ti 5 O 12 anode have a good retention over 100 cycles.

25 ENERGY STORAGE↗