Bulk Structural Changes Research Articles

Modification of Li3PO4 layer effectively boosting lithium storage and thermal safety performance for LiCoO2 batteries

To meet the demand for high-performance LiCoO2 batteries, it is necessary to overcome challenges such as interface degradation and rapid capacity degradation caused by changes in bulk structure, especially under deep delithiation and high temperature conditions. The ion conductive coating layer of Li3PO4 has been directly modified on the surface of LiCoO2 particles using magnetron sputtering method, significantly improving the lithium storage performance of LiCoO2@Li3PO4 composites. Compared to pure LiCoO2, the modified LiCoO2 sample exhibits obviously better cycle life and high-temperature performance. Especially, under the conditions of 2 and 1 C, the LiCoO2@Li3PO4 electrode delivers excellent cycling performance at high voltage of 4.5 V, with capacity retention rates of 89.7% and 75.7% at room temperature and high temperature of 45 °C, being far greater than those of 12.3% and 29.1% for bare LiCoO2 electrodes. It is discovered that the Li3PO4 coating layer not only effectively enhances interface compatibility and suppresses the irreversible phase transition of LiCoO2, but also further improves the Li+ transport kinetics and significantly reduces battery polarization, ultimately enabling the modified LiCoO2 electrode to exhibit excellent lithium storage performance and thermal safety characteristics under high voltage conditions. Thus, such effective modified strategy can undoubtedly provide an important academic inspiration for LiCoO2 implication.

Clarification of Degradation Mechanisms of the OER Activity of Ir-Based Electrocatalyst with Potentiodynamic Accelerated Stress Test

It is vital to understand the degradation mechanisms for the oxygen evolution reaction (OER) activity under acidic electrolyser operating conditions. To this end, we have studied a commercial benchmark Ir-Oxide electrocatalyst during an accelerated stress test (AST) of potential cycling (2000 cycles at 100 mV s−1) between 1.0 and 1.7 V in 0.1 M HClO4. The OER activity degradation (>60%) has been investigated due to (i) bulk structure changes from metal dissolution, (ii) particle growth and, (iii) surface chemical state changes. Microscopic images of the Ir-Oxide catalyst before and after the AST show no significant change in the particle size or agglomeration; moreover, negligible mass loss of the element. Therefore, the OER activity degradation is found to be dominantly (99%) associated with changes of the surface chemical state of Ir, i.e., increase in the Ir4+/Ir3+ ratio at the surface of Ir-Oxide during the AST.

Does Anisotropic ‘Lattice’ Collapse Always Lead to Cracking in Ni-Rich Layered Oxide Cathode Particles?

Single-crystalline Ni-rich layered oxides (LiNi x Mn y Co1−x−y O2; x ≥ 0.8) are promising high-energy-density cathodes for future Li-ion batteries as they can withstand cathode particle cracking, which is a significant contributor to electrochemical capacity loss. The absence of grain/particle boundaries substantially mitigates the build-up of bulk structural strain in these materials generated from the anisotropic structural evolution (i.e., lattice collapse) during electrochemical cycling. However, compared to their polycrystalline counterparts, rigorous evaluations of their long-term electrochemical performance and their dependence on electrode structure changes, impedance, and particle cracking, are still necessary to take it towards commercialisation. Operando X-ray diffraction (XRD) and absorption spectroscopy (XAS) are ideal probes of these bulk electrode structure properties and provide a direct temporal correlation between the battery electrochemistry and the non-equilibrium structural changes in the electrodes. However, such studies often use electrochemically compromised cells modified for X-ray transmission that are neither representative of a real-world full-cell architecture nor operable long-term under industrially relevant cycling conditions, thereby compromising the results' practicality. This is especially problematic for technologically mature cathodes like single-crystalline Ni-rich layered oxides, which require greater scrutiny of their long-term degradation modes after hundreds of cycles. In this work, using in-house operando X-ray studies and large-area post-mortem electron tomography of a (TRL-5) pilot-line-built A7 pouch full cells with industry-relevant specifications, we demonstrate how single-crystalline LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes can withstand the severe anisotropic structural evolution and show no particle cracking even when cycled under harsh conditions of 2.5–4.4 V at 40 °C for 100 cycles. The bulk structural changes in both electrodes as well as the associated electrochemical performance loss are also evaluated. Furthermore, the validity of the in-house pilot line cell results is benchmarked against a commercially sourced Li-ion cell. In addition to furthering our understanding of single-crystalline Ni-rich cathodes, this work emphasises the need for real-world-relevant reproducible fundamental investigations of academic Li-ion cells and presents a methodology for doing so. Figure 1

Synthetic Tailoring of Ionic Conductivity in Multicationic Substituted, High-Entropy Lithium Argyrodite Solid Electrolytes.

Superionic conductors are key components of solid-state batteries (SSBs). Multicomponent or high-entropy materials, offering a vast compositional space for tailoring properties, have recently attracted attention as novel solid electrolytes (SEs). However, the influence of synthetic parameters on ionic conductivity in compositionally complex SEs has not yet been investigated. Herein, the effect of cooling rate after high-temperature annealing on charge transport in the multicationic substituted lithium argyrodite Li6.5[P0.25Si0.25Ge0.25Sb0.25]S5I is reported. It is demonstrated that a room-temperature ionic conductivity of ∼12 mS cm-1 can be achieved upon cooling at a moderate rate, superior to that of fast- and slow-cooled samples. To rationalize the findings, the material is probed using powder diffraction, nuclear magnetic resonance and X-ray photoelectron spectroscopy combined with electrochemical methods. In the case of moderate cooling rate, favorable structural (bulk) and compositional (surface) characteristics for lithium diffusion evolve. Li6.5[P0.25Si0.25Ge0.25Sb0.25]S5I is also electrochemically tested in pellet-type SSBs with a layered Ni-rich oxide cathode. Although delivering larger specific capacities than Li6PS5Cl-based cells at high current rates, the lower (electro)chemical stability of the high-entropy Li-ion conductor led to pronounced capacity fading. The research data indicate that subtle changes in bulk structure and surface composition strongly affect the electrical conductivity of high-entropy lithium argyrodites.

Halide Remixing under Device Operation Imparts Stability on Mixed‐Cation Mixed‐Halide Perovskite Solar Cells

Mixed-halide mixed-cation hybrid perovskites are among the most promising perovskite compositions for application in a variety of optoelectronic devices due to their high performance, low cost, and bandgap-tuning capabilities. Instability pathways such as those driven by ionic migration, however, continue to hinder their further progress. Here, an operando variable-pitch synchrotron grazing-incidence wide-angle X-ray scattering technique is used to track the surface and bulk structural changes in mixed-halide mixed-cation perovskite solar cells under continuous load and illumination. By monitoring the evolution of the material structure, it is demonstrated that halide remixing along the electric field and illumination direction during operation hinders phase segregation and limits device instability. Correlating the evolution with directionality- and depth-dependent analyses, it is proposed that this halide remixing is induced by an electrostrictive effect acting along the substrate out-of-plane direction. However, this stabilizing effect is overwhelmed by competing halide demixing processes in devices exposed to humid air or with poorer starting performance. The findings shed new light on understanding halide de- and re-mixing competitions and their impact on device longevity. These operando techniques allow real-time tracking of the structural evolution in full optoelectronic devices and unveil otherwise inaccessible insights into rapid structural evolution under external stressconditions.

(Invited) Thermal Properties of NMC Cathode Materials

NMC (LiNixMnyCozO2; x+y+z»1) materials deliver high capacity and excellent performance when used as cathodes in lithium-ion batteries. Increasing demand for higher energy density and concerns about the cost and ethics of using cobalt have prompted battery manufacturers to use Ni-rich formulations such as LiNi0.6Mn0.2Co0.2O2 (NMC622) and LiNi0.8Mn0.1Co0.1O2 (NMC811). The thermal stability of (partially) delithiated NMCs is known to decrease with increasing Ni content, however, so that scenarios of fires and other safety events become more distinct possibilities. To investigate the thermal properties of Ni-rich NMCs, we prepared partially and fully delithiated Ni-rich NMCs corresponding to various states-of-charge by chemical methods. We then studied the bulk and surface properties of these materials as they were heated or after they were heated, using a variety of ex situ and in situ synchrotron methods to understand the chemical changes that occur. Of particular concern are reactions that result in release of oxygen. Heated materials progress through a series of bulk structural changes from layered to spinel to rock salt as temperatures rise. Transition temperatures depend on both lithium and nickel content, with bulk changes evident at temperatures as low as 150°C. Surface-sensitive techniques such as soft X-ray absorption spectroscopy (sXAS) indicate that subtle changes that lead to oxygen release can happen well below these temperatures. The thermal behavior of the Ni-rich materials is very complex, and involves lattice transformation, transition metal migration and valence change and lithium redistribution. Moreover, these changes are dependent upon primary particle size, with smaller particles reacting at lower temperatures than larger ones. These observations suggest that materials can be engineered (through primary particle size manipulation, for example) to improve thermal robustness, and therefore, safety and reliability of lithium-ion batteries.

Small Molecule Sorting: A Fluorescence Study of Microemulsions.

The application of microemulsions to a wide range of industries relies on their ability to solubilize small molecules with vastly different structures. Herein, we use multiple fluorescence techniques to probe ionic (rhodamine 6g, r6g), polar (coumarin 153, c153), nonpolar (diphenylanthracene, DPA), and amphiphilic (laurdan) small molecules in a nonionic, bicontinuous microemulsion of varying hydration. All fluorophores investigated were found to associate with the surfactant region despite their different structures and properties. The hydration of the surfactant layer was found to increase linearly with water addition, but while this initially increases the fluidity of the surfactant layer, fluorescence anisotropy of c153 and r6g indicates a stiffening of the surfactant at water content >60%. This stiffening of the surfactant layer at higher water content correlates with a morphological change in the microemulsion from a bicontinuous structure to droplets. In contrast, the nonpolar DPA shows a change in partitioning as hydration changes, increasing its association with the oil domain. Overall, these studies elucidate not only the capability of these microemulsions to host a range of small molecules in the surfactant layer with tunable position but also the ability to probe the driving force of bulk structural changes in these heterogeneous fluids.

Work function of the oxygen functionalized graphenic surfaces – Integral experimental and theoretical approach

The effect of oxygen plasma functionalization of graphenic surface was thoroughly investigated experimentally (SEM, XPS, Raman spectroscopy, work function measurements, TG) and corroborated by DFT molecular modeling using periodic slabs (work function, surface dipoles, EF/DOS). It was found that the introduction of oxygen substantially modified the electrodonor properties of the graphenic surface and the work function changed in a non-monotonous way upon the plasma treatment time. At the short contact time (5–30 s) the work function significantly increased from 4.2 eV (parent graphenic surface) to 5.6 eV and after passing the maximum value it reached plateau at the level of 5.2 eV after 100–150 s. The XPS revealed that the plasma treatment leads to an increase in the oxygen surface concentration (up to ∼10 at.%). A comparison of SEM images and Raman spectra of unmodified and plasma-modified graphenic surfaces indicated that the induced changes are limited to the outermost surface. Indeed, the TGA stability profiles did not indicate any bulk structural changes. Based on the experimental and DFT results, the molecular models of the surface modification process was proposed taking into account the various location of surface oxygen functionalities. At the early stage of the plasma treatment, a generation of strongly polar surface functional groups (surf-OH with the local dipole moment of2.7 D) leads to the formation of an electrostatic potential barrier for electron transfer from the surface (observed increase in work function). Prolonging modification results in the insertion of oxygen heteroatoms into the carbon surface, more uniform electron density distribution, and hence work function decrease. Since the electronic properties of graphenic materials play a key role in their various applications, the obtained results provide rational guidelines for their design and optimization.

Electrochemical proton insertion modulates the hydrogen evolution reaction on tungsten oxides.

The development of new electrocatalysts for the hydrogen evolution reaction (HER) could reduce the dependence on Pt and other rare metals and enable large-scale production of hydrogen with near-zero carbon emissions. Mechanistic insight into the electrocatalytic activity of a material helps to accelerate the development of new electrocatalysts. Alternative electrocatalyst materials such as transition metal oxides and sulfides can undergo insertion reactions that change their properties. Recent reports indicate that the presence of inserted ions can influence the electrocatalytic activity. Here, we utilized a materials chemistry approach to understand the role of proton insertion in the HER activity of the layered tungsten oxide hydrates (WO3·xH2O, x = 1, 2). We synthesized a series of tungsten oxide hydrates along with an octylamine-pillared tungsten oxide (OA-WO3). We used cyclic voltammetry to study the electrochemical reactivity of each material and performed ex situ x-ray diffraction and Raman spectroscopy to understand bulk and surface structural changes during electrochemical cycling. We show an inverse relationship between the degree of proton insertion and HER overpotential in tungsten oxides: the lack of proton insertion leads to a high overpotential for the HER. We discuss three hypotheses for how proton insertion leads to the HER activity in WO3·xH2O: (1) proton insertion changes the electronic band structure of WO3·xH2O, (2) the presence of bulk protons can influence ΔGH,ads at the surface sites, and (3) the inserted protons may participate in the HER mechanism on WO3·xH2O. Overall, this work shows the critical role of proton insertion in enabling the high HER activity in tungsten oxides.

Uncovering Phase Transformation, Morphological Evolution, and Nanoscale Color Heterogeneity in Tungsten Oxide Electrochromic Materials

The electrode–electrolyte interfacial chemistry determines the durability of electrochromic devices. The long‐term cycling stability of transition metal (TM) oxide electrochromic films in the acidic electrolyte is impoverished, which is a major obstacle towards deep market penetration through sustainable and cost-effective smart windows. The research interest in nanostructuring TM oxide films to improve electrochromic performance has grown rapidly. However, there are few fundamental studies that investigate the mechanism of electrochromic degradation. In this work, we revisit the classical tungsten trioxide (WO3) materials as the platform to uncover the previously unknown interrelationship between morphological evolution, phase transformation, nanoscale color heterogeneity, and durability in these electrochromic materials. Through synchrotron spectroscopic, microscopic, and imaging characterizations, we experimentally reveal that tungsten dissolution/redeposition and proton-trapping are the two fundamental origins for performance degradation. The WO3–electrolyte interface is reshaped due to the metal dissolution and redeposition during electrochemical cycling. The recurrent redeposition process provokes the in situ crystal growth, which ultimately leads to the phase transformation from the semicrystalline WO3 to a nanoflake-shaped, proton-trapped tungsten trioxide dihydrate (H x WO3·2H2O). Besides, the heterogeneous proton trapping during long-term electrochemical cycling brings about the charge heterogeneity of thin-film electrodes, which further creates a significant degree of nanoscale color heterogeneity. The interaction between phase transformation, morphological evolution, and nanoscale color heterogeneity results in degraded cycling durability, including inferior optical modulation, switching kinetics, coulombic efficiency, and bleached-state transparency. Our work highlights that the high interfacial reactivity near the electrode surface may be the underlying mechanism for undesired bulk structural changes of electrochromic materials. The overwhelming morphological changes reported here may raise concerns about the legitimacy of a large body of literature that attributes the electrochromic performance solely to initial nanostructure design. More fundamental studies are needed to probe and control the interfacial chemistry in electrochromic and other electrochemical devices.

Understanding the Relationship between State-of-Charge and Structural Fragility in Ni-Rich Layered Materials for Lithium Batteries

Lithium batteries are at the frontier of energy storage. Co-free, Ni-rich layered transition metal oxide (TMO) materials have gained interest within the past decade due to their low cost and increased practical capacity. The challenge with employing these layered oxide cathodes is their inherent structural fragility, facilitated by metal cation migration and lattice oxygen loss. Upon charging, the redox center becomes oxidized, generating thermodynamically favorable electron transfer pathways between the electrolyte and the layered oxide. This transfer pathway is mainly due to the TM3d-O2p orbital hybridization perturbation during battery charging.Surface reconstruction and the structural reordering that accompanies it can undesirably influence the cathode – electrolyte interphase, leading to enhanced electrolyte degradation pathways that can minimize Coulombic efficiency. Electrolyte decomposition occurs at the oxide cathode surface, but can lead to bulk electronic and structural changes of the layered oxide, chemomechanical breakdown, and irreversible phase transformations.In this study, we focus on understanding the interplay between bulk phase transitions and surface instability with respect to electrolyte chemical decomposition. We use novel galvanostatic cycling parameters, extensive electron microscopy, and synchrotron X-ray techniques to decouple chemical and electrochemical electrolyte decomposition pathways to understand their role in Co-free, Ni-rich oxide cathode degradation. This work allows us to decouple surface and bulk chemistries at the cathode – electrolyte interphase to inform further insight into optimal Ni-rich oxide cathode design.

Synergistic Effect of Mn3+ Formation-Migration and Oxygen Loss on the Near Surface and Bulk Structural Changes in Single Crystalline Lithium-Rich Oxides.

Micron-sized single crystal particles could be used to intensify structural changes between bulk and surface area during the charge-discharge process owing to their long-range order. In this study, the effects of Mn3+ formation-migration and oxygen loss on the structure change from the bulk side to the near surface in single crystalline Li1.2Mn0.54Ni0.13Co0.13O2 were decoupled by regulating the voltage windows of 2-4.5, 3-4.8, and 2-4.8 V because Mn3+ formation-migration and oxygen loss mainly occurred below 3 V and beyond 4.5 V, respectively. It is found that oxygen vacancies and phase transformation can be retarded by suppressing the formation-migration of Mn3+. Finally, we also conducted an important insight that boron ion doping in tetrahedral site could be used to suppress Mn3+ migration from octahedral site to tetrahedral site and disrupt the synergistic effect of Mn3+ migration and oxygen loss.

Elucidating the formation pathway of photo-generated asphaltenes from light Louisiana sweet crude oil after exposure to natural sunlight in the Gulf of Mexico

Photooxidation was an important weathering process for spilled oil at the water surface following the Deepwater Horizon oil spill, leading to the rapid formation of polar or oxygenated hydrocarbons, or photo-generated asphaltenes. While the great extent and rapid time scale of this process have been well documented, little is known about the formation pathways and chemical structures of photo-generated asphaltenes. To address this knowledge gap, we conducted a 44-day natural sunlight exposure experiment using Louisiana light sweet crude oil amended in seawater. The saturate, aromatic, resin and asphaltene fractions were separated and quantified by adsorption chromatography. Molecular details were obtained by thermal slicing ramped pyrolysis-gas chromatography–mass spectrometry, while bulk structural changes were quantified by 13C solid-state nuclear magnetic resonance. These analyses illustrate that, in comparison to the “native” petrogenic asphaltenes in crude oil, photo-generated asphaltenes had larger bridged-island structures with smaller aromatic cores and longer alkyl tails in each island. Our results also demonstrated that the large aliphatic fraction of the photo-generated asphaltene was sourced from the alkyl moieties of the aromatic fraction rather than the saturate fraction. A group of intact hydrocarbons, predominantly n-alkanes (C16–C28), was occluded in both native and photo-generated asphaltene matrices. Overall, these results provide insight into the formation mechanisms and structural details of photo-generated asphaltenes in oils after exposure to natural sunlight in Gulf of Mexico waters. This knowledge is valuable for developing remediation strategies for oil spills, in particular those under strong solar irradiance.

Bulk and surface structural changes in high nickel cathodes subjected to fast charging conditions.

A layered oxide cathode, LiNi0.6Mn0.2Co0.2O2, undergoes noticeable crystal expansion by losing significantly higher amounts of Li+ at the end of fast charging cycles. However, the bulk structure of the cycled NMC622 is restored back to its pristine discharged state when intercalated with enough lithium ions during an electrochemical process.

γ-radiation effects on metal oxide particles and their wetted surfaces

ABSTRACTTypical metal oxide corrosion products of structural materials have been irradiated with γ-rays in ultra-pure water to investigate the effect of radiation on the surface oxide and the nature of adsorbed water. Analysis techniques including thermal gravimetric analysis, differential thermal analysis, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy before and after γ-irradiation were employed to investigate surface structural effects and adsorbed water behaviour. The production of H2 in the oxide nanoparticle mixtures was investigated by gas chromatography to probe the mechanism of radiolysis in the water/oxide mixtures and the relationship with surface water. The nature of water at the surface of the oxides was affected by γ-radiation and the relationship was dependent on the particle composition. The rate of H2 production was shown to be oxide dependent, and higher rates of H2 formation were attributed to the decomposition of surface adsorbed water. Changes to the surface chemistry and H2 production rates were found to be highly dependent on the surface chemistry of the metal oxide nanoparticle and no bulk structural changes were observed.

O3-type NaNi1/3Fe1/3Mn1/3O2 layered cathode for Na-ion batteries: Structural evolution and redox mechanism upon Na (de) intercalation

Layered sodium-ion battery cathode, O3-type NaNi1/3Fe1/3Mn1/3O2, has been systematically investigated by synchrotron-based analyses to characterize the structural behavior during electrochemical reaction. X-ray absorption spectroscopy shows reversible redox process upon cycling and clearly proves that both Ni and Fe are active in Na1–xNi1/3Fe1/3Mn1/3O2 and that redox couples of Ni2+/Ni4+via Ni3+ and Fe3+/Fe4+ are responsible for charge compensation. Specifically, the capacity is mainly realized with Ni2+/Ni4+ and slightly from Fe3+/Fe4+ under charging voltage of 4.0 V. At high voltage (>4.0 V), however, Fe redox reaction is dominant and Ni contributes slightly to capacity. In structural evolution, Na1-xNi1/3Fe1/3Mn1/3O2 undergoes phase transformation from O3 to P3 phase below 4.0 V and further reaches OP2 structure above 4.0 V along with a significant contraction of d-spacing. Moreover, quantitative analysis of extended X-ray absorption fine structure suggests that disorder of local structure for Fe is greatly increased in high voltage region. Accordingly, collapse of d-spacing can be considered as being caused by Fe migration in the TM layer into the neighboring Na layer. This study thus provides detailed redox behavior and factor of structural distortions under high voltage region by considering bulk and local structural changes.

Processing, Fast Formation, and Performance of Aqueous-Processed Low-Co Cathodes for High-Energy Lithium-Ion Pouch Cells

Ni-rich, or low-Co, layered active materials are promising candidates for next-generation cathodes for lithium-ion batteries. However, these materials present processing and performance challenges such as compatibility with water during aqueous electrode formulation, unoptimized SEI/CEI formation conditions during cell assembly, and unstable capacity fade when cycled to upper cutoff voltages above 4.3 V vs. Li/Li+. The DOE Battery Manufacturing R&D Facility at ORNL (BMF) has recently moved towards low-Co-containing and high-energy LiNi0.8Mn0.1Co0.1O2 (NMC 811) as a new internal cathode baseline and away from LiNi0.5Mn0.3Co0.2O2 NMC 532 for conducting cathode water stability and formation protocol studies. These XRD, Raman spectroscopy, XPS, and TEM studies verified that there was no change in bulk structure of the NMC 811 with long-term water exposure, and only small changes in the surface chemistry. Capacity retention under 0.33C/-0.33C USABC long-term cycling for NMC 811 aqueous-processed single-layer pouch cells was obtained and compared to: 1) the NMP/PVDF processed standard; and 2) NMC 811 exposed to water for 4 hours before processing with the standard NMP/PVDF formulation. The water exposed NMC 811 processed in NMP showed a similar capacity fade to the aqueous processed case. However, all three cases showed excellent capacity retention through 600 cycles, and the aqueous processed cells and NMP processed cells exhibited ~75% and ~80% capacity retention through 1000 cycles, respectively. It was also observed that the differences in capacity fade for all three cases occur within the first ~100 cycles, and the capacity fade slopes were similar from that point on. It is thought that this slight difference in early capacity retention is due to surface chemistry changes of the NMC 811 during aqueous processing and could be remedied with shorter mixing times or a surface protective coating. To decrease the high manufacturing cost associated with long formation times for low-Co cathodes, five different formation protocols were studied using graphite anodes where the total formation time varied from 10 to 86 h. Electrochemical characterization and post mortem analysis showed that longer formation times do not necessarily improve long-term performance while extremely short formation protocols result in lithium plating and poorer electrochemical performance. It was found that the optimum formation protocol is intermediate in length to minimize impedance growth, improve capacity retention, and avoid lithium plating. This presentation will focus on recent ORNL advancements in these areas, where aqueous processing conditions (mixing times, water exposure, binder type, etc.) and fast formation protocols are being developed for NMC 811 and that will be extended to other low-Co and Co-free cathodes.

Formation of nanocrystalline alloys after Cu ions implantation into amorphous precursor

Abstract Amorphous precursors of A: (Fe64Co21B15)95P4Cu1 and B: (Fe64Co21B15)96P4 alloys were used. Nanocrystalline structure was created by heat treatment. Samples were studied by Mössbauer spectroscopy, XRD and AFM. Cu ions of dose 1016 at/cm2 were implanted into the amorphous B. According to simulated program we estimated that Cu ions created surface layer with a thickness of a few micrometres. Changes in bulk structure were not observed at parameters of Mössbauer spectra after implantation. After heat treatment the implanted sample was nearly identical with the nanocrystalline sample of A. Implantation had an influence on the volumetric fraction of the constituent phases and on their magnetic microstructure. Implantation of Cu ions in amorphous precursor containing Cu as A caused after heat treatment in nanocrystalline state increasing of nanocrystalline component. This technology of preparation of nanocrystalline alloys indicate that implantation of ions into an amorphous precursor has an influence on the final structure and properties of nanocrystalline alloy.

Water-Processable P2-Na0.67Ni0.22Cu0.11Mn0.56Ti0.11O2 Cathode Material for Sodium Ion Batteries

Sodium ion batteries offer a low-cost, sustainable, and environment-friendly solution to large-scale electrochemical energy storage systems. Layered oxides represent a family of promising cathode materials with a potential to improve the energy and power densities while reducing the material cost of sodium ion batteries. However, due to the chemical and structural instability of layered oxides in an aqueous solution, the current battery electrode manufacturing requires expensive and hazardous organic solvents, which impedes the full benefit of the low-cost, sustainable, and eco-friendly advantages. We need an effective technology that empowers a cathode with water processable properties. In this study, we set a representative example, P2-Na0.67Ni0.22Cu0.11Mn0.56Ti0.11O2, to explore its performance under water-processing conditions. This material achieves a discharge capacity of 180 mAh/g and a discharge energy of 544 Wh/kg at 22°C. The aging experiments indicate its superior stability against water, having negligible bulk structural or chemical changes. The surface sensitive soft X-ray absorption spectroscopy shows that the P2-Na0.67Ni0.22Cu0.11Mn0.56Ti0.11O2 has stable surface chemistry in the aqueous solution. Moreover, the cells with water-processed cathodes delivered stable cycling performance with minor voltage decay, originating from the decreased cell impedance. Therefore, the present study sets a refined example to establish a low-cost, sustainable, and eco-friendly solution by developing water-processable electrode materials for sodium ion batteries.

A hydrated amorphous iron oxide nanoparticle as active water oxidation catalyst

Developing efficient water oxidation catalysts (WOCs) with earth-abundant elements still remains a challenging task for artificial photosynthesis. Iron-based WOC is a promising candidate because it is economically cheap, little toxic and environmentally friendly. In this study, we found that the catalytic water oxidation activity on amorphous iron-based oxide/hydroxide (FeOx) can be decreased by an order of magnitude after the dehydration process at room temperature. Thermogravimetric analysis, XRD and Raman results indicated that the dehydration process of FeOx at room temperature causes the almost completely loss of water molecule with no bulk structural changes. Based on this finding, we prepared hydrated ultrasmall (ca. 2.2 nm) FeOx nanoparticles of amorphous feature, which turns out to be extremely active as WOC with turnover frequency (TOF) up to 9.3 s−1 in the photocatalytic Ru(bpy)32+-Na2S2O8 system. Our findings suggest that future design of active iron-based oxides as WOCs requires the consideration of their hydration status.