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All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Reaction Mechanism of Electrodeposited ε-MnO 2 : A Proton-Centered Pathway in Aqueous Zn-Ion Systems

Aqueous Zn/MnO 2 batteries have garnered significant interests owing to their abundance, high theoretical specific capacity, safety, and low cost. However, large-scale application of these systems is limited by the incomplete understanding of the MnO 2 reaction chemistry. The different crystal lattice structures among MnO 2 polymorphs contribute to the variations in reported reaction mechanisms. Among them, ε-MnO 2 polymorph, the dominant phase in electrolytic manganese dioxide (EMD), is notably observed during the charge cycles of aqueous Zn/MnO 2 batteries. Here, in this work, we investigate the electrochemical behavior of an ε-MnO 2 cathode synthesized via electrodeposition from a ZnSO 4 and MnSO 4 electrolyte, onto a 3-dimensional carbon cloth substrate. Proton intercalation emerges as the dominant charge storage mechanism, critically enabling the reversibility of ε-MnO 2 during cycling, as revealed by operando synchrotron X-ray diffraction and X-ray absorption spectroscopy. Additionally, a proton-coupled dissolution/redeposition pathway operates alongside minor Zn 2+ intercalation, as quantified by Rietveld refinement. Morphological and chemical heterogeneities are studied by transmission X-ray microscopy further validates this reaction mechanism. These mechanistic insights provide the foundation for rationally designing Zn/MnO 2 batteries with optimized proton dynamics and charge transfer, advancing these systems as a viable solution for safe, cost-effective grid-scale energy storage.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A two-electron transfer mechanism of the Zn-doped δ-MnO 2 cathode toward aqueous Zn-ion batteries with ultrahigh capacity

Neutral aqueous zinc-ion batteries (ZIBs) have attracted considerable attention due to their safe and green features. As one typical cathode, birnessite MnO 2 (δ-MnO 2 ) suffers from low conductivity and structural instability, and its energy storage mechanism is still not well established yet. Herein, we developed a Zn-doped δ-MnO 2 material via a facile and effective microwave-assisted method for the cathode in aqueous ZIBs. By incorporating Zn to modify the microstructure and promote reaction kinetics, the Zn-doped δ-MnO 2 electrode demonstrates significantly enhanced electrochemical performance with an ultrahigh reversible capacity of 455 mA h g –1 and excellent specific energy of 628 W h kg –1 . In addition, the successive insertion of H + and Zn 2+ and deep two-electron transfer routes are revealed systematically by ex situ experiments. In this study, the two-electron transfer route (Mn 4+ /Mn 3+ and Mn 3+ /Mn 2+ ) mechanism of Zn-doped δ-MnO 2 electrodes explains the exceedingly high capacity and opens new opportunities to develop high-energy aqueous ZIBs.

25 ENERGY STORAGE↗
DOE OSTI2024

Magnetic structure and properties of the compositionally complex perovskite (Y 0.2 La 0.2 Pr 0.2 Nd 0.2 Tb 0.2 )MnO 3

Large configurational disorder in compositionally complex ceramics can lead to unique functional properties that deviate from traditional rules of alloy mixing. In recent years, compositionally complex oxides (CCOs) have shown intriguing magnetic behavior including long-range order, enhanced magnetic exchange couplings, and mixed phase magnetic structures. This work focuses on how large local spin disorder affects magnetic ordering in a CCO. Specifically, we investigated the A-site alloyed perovskite, (Y 0.2 La 0.2 Pr 0.2 Nd 0.2 Tb 0.2 )MnO 3 , or (5A)MnO 3 , using a combination of bulk magnetometry, synchrotron X-ray diffraction, and temperature-dependent neutron diffraction. The five A-site ions have an average spin and ionic radius nearly equal to that of Nd 3+ ions, which minimizes structural distortions and allows for an understanding of the local spin disorder effects through a direct comparison with NdMnO 3 . Our magnetometry data show that (5A)MnO 3 exhibits two distinct phase transitions associated with the A-site and B-site sublattices, as seen in NdMnO 3 , as well as the presence of domain pinning and exchange bias at low temperature, suggesting a mixed phase magnetic ground state, as seen in other magnetic CCOs. Neutron powder diffraction shows clear long-range antiferromagnetic ordering below 67 K and refines to a Pn'ma' magnetic structure at low temperature, in excellent agreement with the well-studied behavior of NdMnO 3 . The two most notable differences in (5A)MnO 3 magnetism apparent from our data are a slight suppression of the B-site ordering temperature, which is explained by a smaller Mn–O–Mn bond angle in (5A)MnO 3 than NdMnO 3 , and the presence of a magnetic susceptibility transition above the B-site ordering, which could indicate the formation of a cluster glass but requires further study. Finally, this work demonstrates a general method of isolated investigation of size and spin disorder in CCOs and motivates future work using local structure probes to better understand the effects of nanoscale clustering and local spin disorder in magnetic CCOs.

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

Imaging Cycle-Induced Damage of MnO 2 Microparticles

MnO 2 has been proposed as an electrode material in electrochemical energy storage devices. However, poor cycle life, especially in aqueous electrolytes, remains a detriment to commercialization. Prior studies have suggested a number of explanations for this capacity loss; however, experiments aimed at elucidating the details of the degradation process (es) are sparse. We describe here a microtube-membrane construct that allows for electrodeposition of monodisperse MnO 2 microparticles distributed across the membrane surface, and for subsequent electrochemical cycling of these MnO 2 particles. This allowed for a detailed analysis of the effect of cycling on the MnO 2 , by simply imaging the membrane surface before and after cycling. When an aqueous electrolyte was used, gross changes in particle shape, size and morphology were observed over the course of 500 cycles. Partial dissolution occurred as well. No such changes were observed when the MnO 2 particles were cycled (up to 500 times) in a propylene carbonate electrolyte solution.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Isothermal Microcalorimetry Analysis of Li/ β -MnO 2 Discharge

Despite widespread use over several decades, the lithium/manganese dioxide (Li/MnO 2 ) discharge mechanism is not completely understood owing to the structural complexity of the material. However, an improved understanding could lead to broader adoption as a primary and even secondary cathode material. Here, we examine the discharge of single-phaseβ-MnO 2 using isothermal microcalorimetry for the first time. Equilibrium voltage and entropy changes are characterized over the entire discharge range and used to rationalize the results. These measurements are supplemented by electrochemical impedance and X-ray diffraction data that give the clearest picture of theβ-MnO 2 lithiation process to date. We find that the first half of discharge is dominated by a two-phase reaction to form Li 0.5 MnO 2 followed by single-phase insertion to a composition of Li 1.0 MnO 2 , which confirms prior first-principles calculations. The tetragonalβ-MnO 2 lattice undergoes asymmetric expansion from Jahn-Teller distorted Mn 3+ to form an orthorhombic LiMnO 2 phase which retains the 1 × 1 tunnel structure. Microcalorimetry results suggest the presence of parasitic reactions occurring during the second half of discharge, which could arise from decomposition of electrolyte or release and reaction of residual water retained in the structure.

Electrochemistry↗
DOE OSTI2021

Atomistic Insights of Irreversible Li + Intercalation in MnO 2 Electrode

Tunnel-structured MnO 2 represents open-framed electrode materials for reversible energy storage. Its wide application is limited by its poor cycling stability, whose structural origin is unclear. We tracked the structure evolution of β-MnO 2 upon Li + ion insertion/extraction by combining advanced in situ diagnostic tools at both electrode level (synchrotron X-ray scattering) and single-particle level (transmission electron microscopy). The instability is found to originate from a partially reversible phase transition between β-MnO 2 and orthorhombic LiMnO 2 upon lithiation, causing cycling capacity decay. Moreover, the MnO 2 /LiMnO 2 interface exhibits multiple arrow-headed disordered regions, which severely chop into the host and undermine its structural integrity. Our findings could account for the cycling instability of tunnel-structured materials, based on which future strategies should focus on tuning the charge transport kinetics toward performance enhancement.

25 ENERGY STORAGE↗
DOE OSTI2023

Evidence of redox cycling as a sub-mechanism in hydrogen production during ethanol steam reforming over La 0.7 Sr 0.3 MnO 3-x perovskite oxide catalysts

Ethanol steam reforming (ESR) is of societal interest. Here, in this work, experiments were conducted to ascertain if some of the H 2 is produced by a redox cycle involving H 2 O filling oxygen vacancies over reducible oxide catalysts. Redox cycling experiments were performed over La 0.7 Sr 0.3 MnO 3-x (100) in ultra-high vacuum. It was found that H 2 was produced from redox cycling with alternating ethanol and water exposures over La 0.7 Sr 0.3 MnO 3-x (100), with both half-cycles occurring at temperatures ≤800 K. In the first half-cycle, ethanol ‘directly’ reduced the surface to create oxygen vacancies (not by a CO intermediate), and in the second half-cycle water filled oxygen vacancies to make H 2 . The H 2 production during the water exposure has a half-cycle turnover frequency of >3.2 × 10 -2 molecules site -1 s -1 in the temperature range of 700–800 K, which is fast enough to be part of the ESR full catalytic cycle. Flowing both reactant gases together, ethanol and water, over La 0.7 Sr 0.3 MnO 3-x (100) and La 0.7 Sr 0.3 MnO 3-x powders significantly increases hydrogen production compared to pure ethanol. The results suggest that steady state ESR includes a sub-mechanism of ethanol ‘directly’ reducing the surface to create oxygen vacancy, and water filling oxygen vacancy to make some of the H 2 by a Mars van Krevelen type mechanism.

08 HYDROGEN↗
DOE OSTI2020

Rooting MnO 2 into protonated g-C 3 N 4 by intermolecular hydrogen bonding for endurable supercapacitance

Composited electrode materials for energy storage typically benefit from the merits of each component but meanwhile largely suffer from the vulnerable structural integrity during repetitive cycling. Realizing the merely physical attachment in most composited structures being too weak to survive harsh cycling, we report here a facile one-step synthesis strategy with generation of chemical bonds, more specifically, intermolecular hydrogen bonds, to tightly combine each component. Here, we demonstrate this concept by designing a composite featuring MnO 2 nanorods chemically rooted into protonated g-C 3 N 4 , where the protonation of 2D g-C 3 N 4 substrate (pg-C 3 N 4 ), the nucleation/growth of MnO 2 and the formation of hydrogen bonding between pg-C 3 N 4 and MnO 2 simultaneously occur. The obtained composite, when applied for supercapacitive energy storage, yields maximum specific capacitances of 348.4 F·g -1 at a current density of 1.0 A·g -1 as well as a high retention of ~85.0% after 10000 cycles at 6.0 A·g -1 , surpassing most previously reported composited electrode materials based on either MnO 2 or g-C 3 N 4 . Finally, we expect this work to inspire the synthesis of composited electrode materials with consolidated 3D architecture for endurable energy storage performance.

25 ENERGY STORAGE↗
DOE OSTI2023

Effects of Ball Milling on the Electrochemical Capacity and Interfacial Stability of Li 2 MnO 3 Cathode Materials

The cycling mechanism of Li 2 MnO 3 cathode materials synthesized by conventional solid-state methods at high temperatures (800-900 °C) has been intensively investigated. Previous studies showed that CO 2 and O 2 gas evolution accounts for most of the charge capacity, followed by some Mn reduction during discharge. In this work, we analyze the effects of ball milling on the structure, surface contaminant, and electrochemical capacity of Li 2 MnO 3 cathode material, with or without a graphitic fluoride (C-F) additive. At the same time, C-F is added to form a protective coating layer that reduces unwanted reactions with the electrolyte during later electrochemical cycling. We find that the C-F ball-milled material shows Li 2 MnO 3 /LiMnO 2 composite phases, while the purely ball-milled material shows a single Li 2 MnO 3 phase. Furthermore, we characterize surface species and gas evolution during the first cycle, which reveals the decomposition of Li 2 CO 3 and the carbonate electrolyte during the first charge, especially during the high potential region (>4.4 V), and the electrochemical reduction of only a small fraction of the evolved gas on the first discharge (<2.75 V). The appearance further demonstrates the repetitive nature of this process during charge and disappearance during discharge of Mn 2p 3/2 X-ray photoelectron spectroscopy (XPS) spectra signals during the first two cycles. These processes result in first discharge specific capacities of only 155 and 170 mAh/g after first charge specific capacities of 210 and 320 mAh/g for the pure ball-milled and ball-milled with C-F materials, respectively. These studies demonstrate the interfacial instability introduced by ball milling. However, the electrochemical capacity is significantly increased, necessitating further investigation to determine whether ball milling can activate Mn-containing cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2021

Discharging Behavior of Hollandite α-MnO 2 in a Hydrated Zinc-Ion Battery

Hollandite, α-MnO 2 , is of interest as a prospective cathode material for hydrated zinc ion batteries (ZIBs); however, the mechanistic understanding of the discharge process remains limited. Herein, a systematic study on the initial discharge of α-MnO 2 cathode under hydrated environment was reported using density functional theory (DFT) in combination with complementary experiments, where the DFT predictions well described the experimental measurements on discharge voltages and manganese oxidation states. According to the DFT calculations, both protons (H + ) and zinc ions (Zn 2+ ) contribute to the discharging potentials of α-MnO 2 observed experimentally, where the presence of water plays an essential role during the process. This study provides valuable insights into the mechanistic understanding of the discharge of α-MnO 2 in hydrated ZIBs, emphasizing the crucial interplay among the H 2 O molecules, the intercalated Zn 2+ or H + ions, and the Mn 4+ ions on the tunnel wall to enhance the stability of discharged states and, thus, the electrochemical performances in hydrated ZIBs.

25 ENERGY STORAGE↗
DOE OSTI2021

Exemption of lattice collapse in Ni–MnO 2 birnessite regulated by the structural water mobility

Lattice collapse and associated mechanical fracture frequently occur in Li-intercalated metal oxide cathodes at the deep charge state upon Li-ion removal, governed by chemical compositions and the resulting electron density of the oxygen atoms. However, similar lattice collapse for metal oxide electrodes in aqueous storage and its mitigation have not been well studied. In this work, we reported the lattice collapse of MnO 2 layered birnessite during the aqueous de-sodiation process at high voltage due to the structural water motion, as evidenced by in situ XRD. Unlike non-aqueous Li-intercalated electrodes, Ni-dopants mitigated the lattice collapse of birnessite at deep charge states. Moreover, density functional theory (DFT) calculations showed that Ni doping induces charge depletion of lattice oxygen due to its higher electronegativity than Mn. This charge reduction, in turn, yields a significant decrease in electrostatic repulsion between the oxygens belonging to lattice and structural water. Classical molecular dynamics simulations based on atomic charges obtained from DFT elucidate that Ni-doping facilitates immobilization of structural water in (Ni)MnO 2 and prevents lattice collapse upon Na-ion removal. (Ni)MnO 2 exempted from lattice collapse shows an improved storage capacity relative to MnO 2 while maintaining similar cycling stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Revealing short- and long-range Li-ion diffusion in Li 2 MnO 3 from finite-temperature dynamical mean field theory

Li 2 MnO 3 is a key component of Li-excess layered cathodes of the form (1 − x), LiMO 2 + x, Li 2 MnO 3 (M = Mn, Ni, Co, …), yet its role in setting Li-ion transport limitations remains under debate. Here, in this study, we combine DFT+U, finite-temperature DFT+DMFT with a continuous-time quantum Monte Carlo impurity solver, and nudged-elastic-band (NEB) calculations to study Li + migration in paramagnetic Li 2 MnO 3 in the presence of a single Li vacancy. Evaluating DMFT total energies along the DFT+U NEB geometries reveals that dynamical correlations strongly renormalize the lowest-barrier processes, reducing the activation energies to E a = 0.18 eV for the shortest-range hop and E a = 0.50 eV for the next-lowest (transport-controlling) step. The 0.18 eV barrier quantitatively reproduces the short-range activation energy from µ+SR, while the 0.50 eV barrier is consistent with the long-range transport scale extracted from ac-impedance measurements. This single-vacancy, paramagnetic DMFT description thus provides a unified interpretation of local and macroscopic probes without invoking clustered vacancy configurations or strong extrinsic disorder, consistent with nearly stoichiometric Li 2 MnO 3 powders. More broadly, our results highlight finite-temperature dynamical correlations as an essential ingredient for predicting ionic migration energetics in correlated oxide electrodes.

Lee, Alex Taekyung [University of Illinois, Chicag↗
DOE OSTI2023

Weak trimerization in the frustrated two-dimensional triangular Heisenberg antiferromagnet Lu y Y 1-y MnO 3

To understand the 2D triangular Heisenberg antiferromagnetic system, we investigated the magnetic structures and the dynamics of Lu y Y 1-y MnO 3 in detail. The substitutions are adjusted to the Mn atomic position close to x Mn =$\frac{1}{3}$. The neutron powder diffraction data claims that the magnetic structure of Lu y Y 1-y MnO 3 is described as a mixture of Γ 3 (P6' 3 cm') and Γ 4 (P6' 3 c'm) at the x Mn position for y=0.15, 0.30, and 0.45. The ratio of Γ 3 and Γ 4 depends on temperature and composition and the fraction of Γ 3 increases upon cooling, while no clear trimerization was observed at the xMn position. We estimated exchange parameters from the analysis of the low-energy part of the spin waves. The results showed a weak trimerization effect on cooling because the nearest-neighbor exchange interaction is slightly enhanced. The temperature dependence of the spin-wave dispersion around the Γ point shows that the spin gap closes with increasing temperature because the exchange interactions in the nearest Mn-Mn neighbor become smaller. Gapless diffusive magnetic excitation from a Mn triangular lattice has been observed in a wide range in Q and E space of Lu y Y 1-y MnO 3 . We found that Lu 0.3 Y 0.7 MnO 3 could be an ideal case to investigate the trimerization, frustrated magnetism, and magnetoelastic coupling often observed in two-dimensional triangular lattice Heisenberg antiferromagnet systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Dynamics of disordered intermediates during the two-electron alkaline MnO 2 conversion reaction for grid-scale batteries

Battery technologies beyond Li-ion are likely needed for extensive integration of grid-scale storage. The rechargeable Zn-MnO 2 chemistry has the potential for high sustainability, high safety, and low cost, using Earth-abundant basis materials. In an alkaline electrolyte, the MnO 2 cathode can cycle reversibly if modified by including a Bi-containing additive, although the cycling mechanism remains mostly unknown. This work presents an account of the intermediate species involved in the electrochemical transformation from layered δ-MnO 2 to Mn(OH) 2 and back. During charge, a disordered intermediate with a structure resembling layered β-MnOOH exists stably for an extended period, corresponding to a regime known to have unexpected electrochemical activity of Bi. During discharge, β-MnOOH exists only briefly and is never the majority material, revealing that the cycling mechanism is asymmetric. In conclusion, these findings represent a significant advance in mechanistic knowledge and can enable engineering to develop the system for commercial use.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Magnetic La 0.7 Sr 0.3 MnO 3 Membranes Synthesized by Etching a Sr 3 Al 2 O 6 Sacrificial Layer Using an Intermediary Manganite Protection Layer

The integration of perovskite oxides onto flexible substrates has witnessed significant advancements owing to the development of an epitaxial lift-off technique utilizing a Sr 3 Al 2 O 6 sacrificial layer. However, Sr 3 Al 2 O 6 is susceptible to instability in both air and high-temperature oxygen atmospheres, potentially leading to degradation during the growth of the functional oxide layer. In this study, we investigate the use of an oxygen-deficient La 0.7 Sr 0.3 MnO 3 as capping layer, and demonstrate its ability to stabilize Sr 3 Al 2 O 6 films in ambient air. We successfully synthesized freestanding La 0.7 Sr 0.3 MnO 3 membranes by etching this sacrificial layer and transferring them onto flexible polymer substrates. Importantly, the magnetic properties of the La 0.7 Sr 0.3 MnO 3 films are preserved in these membranes. Furthermore, our results underline that employing a thin manganite capping layer ensures both high structural quality and the preservation of functional properties in the resulting membranes.

Deposition↗
DOE OSTI2023

3D-Printed Graded Electrode with Ultrahigh MnO 2 Loading for Non-Aqueous Electrochemical Energy Storage

Electrolytic manganese dioxide is one of the promising cathode candidates for electrochemical energy storage devices due to its high redox capacity and ease of synthesis. Yet, high-loading MnO 2 often suffers from sluggish reaction kinetics, especially in non-aqueous electrolytes. The non-uniform deposition of MnO 2 on a porous current collectors also makes it difficult to fully utilize the active materials at high mass loading. Here, a 3D printed graded graphene aerogel (3D GA) that contains sparsely separated exterior ligaments is developed to create large open channels for mass transport as well as densely arranged interior ligaments providing large ion-accessible active surface. The unique structural design homogenizes the thickness of electro deposited MnO 2 even at an ultrahigh mass loading of ≈70 mg cm -2 . The electrode achieves a remarkable volumetric capacity of 29.1 mA h cm -3 in the non-aqueous electrolyte. A Li-ion hybrid capacitor device assembled with a graded 3D GA/MnO2 cathode and graded 3D GA/VO x anode exhibits a wide voltage window of 0–4 V and a superior volumetric energy density of 20.2 W h L -1 . The findings offer guidance on 3D printed electrode design for supporting ultrahigh loading of active materials and developments of high energy density energy storage devices.

electrochemical energy storage↗
DOE OSTI2024

Rational optimization of substituted α–MnO 2 cathode for aqueous zinc–ion battery

Density functional theory (DFT) is utilized to explore the effects of increasing concentrations of vanadium (V) and chromium (Cr) substitution on the discharge of α-MnO 2 cathode in hydrated zinc-ion batteries (ZIBs). During H + -intercalation and Zn 2+ -intercalation, Cr-substitution proves to be more effective than V-substitution in promoting discharge behaviors. Transitioning from Mn 0.875 Cr 0.125 O 2 , Mn 0.75 Cr 0.25 O 2 to Mn 0.625 Cr 0.375 O 2 is found to consistently enhance the discharge voltage, along with improved tunnel structure retention and volume expansion suppression. In comparison, the promoting effect of increasing V-substitution is relatively small at initial discharge stages and leads to degradation at later stages, primarily due to an increased concentration of unstable Mn 2+ ion. The superior effect of Cr-substitution is attributed to the unique atomic and electronic structures of substituted Cr 4+ and reduced Cr 3+ ions during discharge. These ions serve as active electron acceptors to limit the formation of Mn 3+ and Mn 2+ ions, and as anchors to stabilize the α-MnO 2 framework and intercalated H + /Zn 2+ ions, respectively. Finally, our study highlights fine-tuning through substitution to enhance the performance of α-MnO 2 -based cathode materials in ZIBs.

25 ENERGY STORAGE↗