Solid Phase Transformation Research Articles

The change of phase composition and the morphology of particles of hydrothermal titanosilicate precipitates during their aging

During the study of phase formation under conditions of hydrothermal synthesis of alkaline titanosilicate systems (NH₄)₂TiO(SO₄)₂⋅H₂O или TiOSO₄⋅H₂O-Na₂SiO₃-NaOH-H₂O it was found that the formed titanosilicate solid phases differ both in composition and structure. The process of their aging under conditions of long-term exposure without forced heating is accompanied mainly by the loss of free water without noticeable structural and morphological changes. The exposure to the temperature of 70–100°С significantly accelerates the process of solid phase transformation. In these conditions, a porous system of particles is formed, which is confirmed by an increase in their specific surface area and total pore volume, as well as by an increase in the activity of the powders to absorb single- and double-charged cations. The effectiveness of hydrochloric acid treatment of fresh and especially aged precipitates on the ordering of the structure with the formation of crystals of a clear frame shape, inherent in the minerals zorite and ivanyukite, which contributes to increasing the sorption capacity of the final product is shown. The obtained results are used to adjust the technological regulations, which are used to test the technology of titanosilicate sorbent on the pilot plant.

Uranium Repartitioning during Microbial Driven Reductive Transformation of U(VI)-Sorbed Schwertmannite and Jarosite.

This study exposes U(VI)-sorbed schwertmannite and jarosite to biotic reductive incubations under field-relevant conditions and examines the changes in aqueous and solid-phase speciation of U, Fe, and S as well as associated microbial communities over 180 days. The chemical, X-ray absorption spectroscopy, X-ray diffraction, and microscopic data demonstrated that the U(VI)-sorbed schwertmannite underwent a rapid reductive dissolution and solid-phase transformation to goethite, during which the surface-sorbed U(VI) was partly reduced and mostly repartitioned to monomeric U(VI)/U(IV) complexes by carboxyl and phosphoryl ligands on biomass or organic substances. Furthermore, the microbial data suggest that these processes were likely driven by the consecutive developments of fermentative and sulfate- and iron- reducing microbial communities. In contrast, the U(VI)-sorbed jarosite only stimulated the growth of some fermentative communities and underwent very limited reductive dissolution and thus, remaining in its initial state with no detectable mineralogical transformation and solid-phase U reduction/repartitioning. Accordingly, these two biotic incubations did not induce increased risk of U reliberation to the aqueous phase. These findings have important implications for understanding the interactions of schwertmannite/jarosite with microbial communities and colinked behavior and fate of U following the establishment of reducing conditions in various acidic and U-rich settings.

Thermal experiment study on the self-luminous properties of metallic iron during solid–liquid phase transition

According to the thermal experiment study of the self-luminescence spectrum of industrially pure iron (DT8) at a heating and cooling rate of 5 °C/min, at the moment of 0 (800 °C), DT8 had no significant self-luminescence characteristics in the wavelength range of 200–1100 nm. At the same time, the first-order differentiation of the spectral intensity versus time was equal to zero at the beginning and end moments of the solid-liquid phase transition. When the solid-liquid melt temperatures are equal (i.e. 1531 °C), there are two sharp peaks at wavelengths of 589.1 nm and 766.7 nm of the self-luminous spectrum in the pure liquid state compared to the self-luminous spectrum in the pure solid state. The intensity of the spectrum decreases significantly as the metallic iron changes from the pure solid phase to the pure liquid phase, with a reduction rate greater than 20%. The appearance of the fitted peaks at 589.1 nm and 769 nm was found by XPS fitting analysis to be a significant feature of the difference in the auto-luminescence spectra of pure solid phase and pure liquid phase metallic iron at a constant melt pool temperature. After the transformation of pure solid phase into pure liquid phase, the decay rate of the self-luminous spectrum in the long-wave direction at wavelengths greater than 762 nm is greater than that in the short-wave direction at wavelengths less than 625 nm.

In Situ Observation of Microstructure and Precipitate Phase Transformation during the Solidification of Mg‐Containing GH3625 Alloy at Different Cooling Rates

In practical applications, intermetallic compounds like Laves phase and metal carbides adversely affect the performance of nickel‐based superalloys. Using a high‐temperature confocal laser scanning microscope, the solidification process of as‐cast GH3625 alloy containing Mg at different cooling rates (−20, −35, and −50 °C min−1) is studied. Fitting curves of the volume fraction of the solid phase with solidification temperature before and after Mg treatment are obtained. Trends of solid phase transformation rates with solidification temperature are determined. Differential scanning calorimetry is employed to analyze and statistically evaluate the melting temperature range and enthalpy of each phase during the melting process. Experimental results demonstrate that Mg treatment significantly accelerates the alloy solidification at the cooling rates of −20 and −35 °C min−1, while reducing the area of residual liquid phase at the same solidification temperature, disrupting the Laves/NbC eutectic relationship, and regularizing NbC morphology, transitioning its distribution from aggregation to dispersion. After Mg treatment, the precipitation of the Laves phase is significantly reduced. As a result, the influence mechanism of Mg treatment on the phase transformation and microstructure of GH3625 is clarified based on homogeneous nucleation theory.

In-situ scattering and calorimetric studies of crystallization pathway and kinetics in a Cu-Zr-Al bulk metallic glass

The crystallization route and kinetics of a Cu-Zr-Al bulk metallic glass (BMG), based on Cu50Zr50, were investigated using in-situ synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS), in-situ high-energy X-ray diffraction (HEXRD), and differential scanning calorimetry (DSC). The acquisition of kinetic diagrams of SAXS/WAXS enables the direct construction of the overall phase transformation route from room temperature to the onset temperature of solid state phase transformation upon heating. It is revealed that the studied alloy undergoes multiple steps (at least five steps) before reaching the high-temperature thermodynamic equilibrium. This is distinct from the commonly believed simple path of glass → Cu10Zr7 + CuZr2 → B2-CuZr predicted by the Cu-Zr equilibrium phase diagram. In addition to thermodynamics, we emphasize that kinetic factors play a prominent role in the phase transformation process of Cu-Zr-Al BMGs. Furthermore, isothermal crystallization kinetics analyses conducted by in-situ HEXRD and DSC indicate that the formation of the initial crystalline phase, specifically the Cu10Zr7, follows an interface-controlled quasi-polymorphic process with an increasing nucleation rate. The findings of this study may provide novel insights into the crystallization mechanism of glass-forming supercooled liquids from a thermophysical perspective.

Lithium extraction via capacitive deionization: AlF3 coated LiMn2O4 spheres for enhanced performance

The escalating demand within the lithium battery sector has intensified the pursuit of efficient methods for lithium's selective extraction from brines. Particularly, LiMn2O4 (LMO) emerges as a prime candidate, celebrated for its robust redox properties and considerable theoretical adsorption capacity. Nonetheless, its application is hampered by structural instability due to Jahn-Teller distortion, which triggers a phase shift from cubic to tetragonal and Mn dissolution, undermining the material's lithium extraction efficiency. In response, this study introduces an innovative, multifunctional amorphous AlF3 coating on LMO spheres, employing a novel synthesis approach combining co-precipitation, solid-phase transformation, and a final AlF3 deposition. This method not only mitigates Mn leaching but also curtails the adverse effects of Jahn-Teller distortion by integrating trace amounts of Al3+ into the LMO lattice, thus fortifying both the surface and bulk structure of the material. Significantly, the AlF3-coated LMO demonstrates an enhanced lithium extraction capacity of 31.5 mg g−1 at 1.2 V with feedwater concentration of 150 mg L−1. Additionally, the optimally coated sample exhibits superior cycling stability, maintaining high-capacity retention and minimal manganese dissolution across multiple absorption-desorption cycles. Furthermore, the optimized electrode exhibits exceptional selectivity for lithium over magnesium in solutions with high Mg2+/Li+ ratios, achieving a notable separation factor of 7.66. Additionally, this electrode demonstrates efficient separation capabilities in synthetic brine, effectively distinguishing Li+ from competing ions such as Na+, K+, Ca2+, and Mg2+, which underscores its substantial potential for effective lithium recovery from complex brines.

Uncovering the Size-Dependent Thermal Solid Transformation of Akaganéite.

Investigating the structural evolution and phase transformation of iron oxides is crucial for gaining a deeper understanding of geological changes on diverse planets and preparing oxide materials suitable for industrial applications. In this study, in-situ heating techniques are employed in conjunction with transmission electron microscopy (TEM) observations and ex-situ characterization to thoroughly analyze the thermal solid-phase transformation of akaganéite 1D nanostructures with varying diameters. These findings offer compelling evidence for a size-dependent morphology evolution in akaganéite 1D nanostructures, which can be attributed to the transformation from akaganéite to maghemite (γ-Fe2O3) and subsequent crystal growth. Specifically, it is observed that akaganéite nanorods with a diameter of ∼50nm transformed into hollow polycrystalline maghemite nanorods, which demonstrated remarkable stability without arresting crystal growth under continuous heating. In contrast, smaller akaganéite nanoneedles or nanowires with a diameter ranging from 20 to 8nm displayed a propensity for forming single-crystal nanoneedles or nanowires through phase transformation and densification. By manipulating the size of the precursors, a straightforward method is developed for the synthesis of single-crystal and polycrystalline maghemite nanowires through solid-phase transformation. These significant findings provide new insights into the size-dependent structural evolution and phase transformation of iron oxides at the nanoscale.

The influence mechanism of fulvic acid on Fe(II)-catalyzed transformation of Cr(III)-bearing schwertmannite: pH effect and nanoscale redistribution of Cr and C

The interactions between schwertmannite (Sch), chromium (Cr), and dissolved organic matter play a significant role in the cycling of Cr and carbon (C) in acid mine drainage (AMD) contaminated soils. However, mechanism insights into the immobilization of Cr and C during the Fe(II)-catalyzed, fulvic acid (FA)-mediated reductive transformation of Cr(III)-bearing Sch (Cr-Sch) remain unclear. In this study, we investigated the mechanisms underlying sequestration of Cr and C during the Cr-Sch transformation under various FA concentrations and pH conditions. Solid-phase transformation analysis revealed that the pH increasing from 3.5 to 7.0 favored the transformation of Cr-Sch to lepidocrocite (Lep) and/or goethite (Goe), while the transformation rate and degree decreased with increasing FA concentration from 10 to 100 mg/L. By means of the distribution of elements observed in spherical aberration corrected scanning transmission electron microscopy, Cr was predominantly adsorbed on the Lep and Goe surfaces, and Cr may be partially sequestered by Goe. Meanwhile, FA was adsorbed onto the surfaces of Goe and Lep, and the incomplete defect structure of Lep provided space for C immobilization. This study provides a basis for an in-depth understanding of the nanoscale mechanisms of Cr and FA redistribution during Cr-Sch transformation and can be used for developing strategies for the immobilization of heavy metals and C in AMD-polluted environments.

LiFe0.3Mn0.7PO4-on-MXene heterostructures as highly reversible cathode materials for Lithium-ion batteries

Two-dimensional (2D) heterostructure materials, incorporating the collective strengths and synergetic properties of individual building blocks, have attracted great interest as a novel paradigm in electrode materials science. The family of 2D transition metal carbides and nitrides (e.g., MXenes) has become an appealing platform for fabricating functional materials with strong application performance. Herein, a 2D LiFe0.3Mn0.7PO4 (LFMP)–on-MXene heterostructure composite is prepared through an electrostatic self-assembly procedure. The functional groups on the surface of MXenes possess highly electronegative properties that facilitate the incorporation of LFMPs into MXenes to construct heterostructure composites. The special heterostructure of nanosized-LiFe0.3Mn0.7PO4 and MXene provides rapid Li+ and electron transport in the cathodes. This LiFe0.3Mn0.7PO4-3.0 wt% MXene composite can exhibit an excellent rate capability of 98.3 mAh g−1 at 50C and a very stable cycling performance with a capacity retention of 94.3 % at 5C after 1000 cycles. Furthermore, NaFe0.3Mn0.7PO4-3.0 wt% MXene with stable cyclability can be obtained by an electrochemical conversion method with LiFe0.3Mn0.7PO4-3.0 wt% MXene. Ex-situ XRD suggests that LiFe0.3Mn0.7PO4-on-MXene achieves a highly reversible structural evolution with a solid solution phase transformation (LFMP→LixFe0.3Mn0.7PO4 (LxFMP), LxFMP→LFMP) and a two-phase reaction (LxFMP←→Fe0.3Mn0.7PO4 (FMP)). This work provides a new direction for the use of MXenes to fabricate 2D heterostructures for lithium-ion batteries.

Strengthening Ti3SiC2/Cu brazed joint assisted with cold spray additive manufacturing: Lower brazing temperature through interdiffusion and graded reinforcement for stress relaxation

Graded composite fillers exhibit unique advantages in alleviating residual stress in ceramic/metal brazed joints. However, traditional methods for preparing graded composite fillers are often complex and may deplete their strengthening phases. In this study, cold spray additive manufacturing was employed to fabricate yttria-stabilized zirconia (YSZ)-Ti25Zr25Ni25Cu25-Ag graded composite coatings on Cu substrates to serve as fillers. The graded composite coatings and the resultant Ti3SiC2/Cu brazed joints were systematically characterized to elucidate the deposition mechanism of the coatings and its residual stress-relaxed mechanism. The bondings between particles in the coatings, based on their plastic deformation ability, were classified into noncrystalline weak bonds and homogeneous strong bonds. Both bondings facilitated the elemental interdiffusion between filler and Cu substrate during the heating process, which contributed to the formation of Ag-Cu eutectic. This significantly reduced the required brazing temperature and its induced residual stress. Furthermore, the solid phase transformation of graded-distributed YSZ within the brazing seam from tetragonal to monoclinic achieved a smooth thermal transition and releasing residual stress at the same time. Consequently, the shear strength of the brazed joint reached to the highest value of 110.23 ± 3.45 MPa, which was Much higher than the previously reported values. This study introduces a novel method for residual stress relaxation assisted with cold spray technology and broadens its application in the brazing field.

Powstawanie polifazowej asamblaży minerałów z grupy platynowców w masywie dunitowo-szonkinitowym Inagli w Aldan Shield na platformie syberyjskiej

The Inagli massif is a concentric-zonal ring massif consisting of a dunite core bordered by a sequential series of peridotites, pyroxenites and shonkinites. In dunites, there are densely disseminated accumulations of chromspinelides, as well as schlieren and veined particles of massive chromitites, to which polyphase growths of platinum-group minerals (PGM) are confined. The Inagli intrusive, like the well-known Konder massif, belongs to an independent "Aldan" type of platinum-bearing deposits. The Aldan type of ring intrusions is a platform analogue of the "Ural-Alaskan" zonal dunite-gabbro massifs of orogenic regions. In placers, dunites and chromitites of the Inagli massif, PGM are mainly represented by isoferroplatinum (Pt3Fe) with an admixture of iridium up to 8 wt %. In isoferroplatinum, symplektitic iridium particles and small inclusions of osmium, laurite, ehrlichmanite, malanite, as well as other sulfides and arsenides of platinum-group elements (PGE) are often observed. The bulk composition of such polymineral aggregates can be calculated based on the volume ratios and chemical composition of individual phases. The results obtained in this way show that the compositions of the initial polycomponent solid solutions vary from Pt-Ir-Fe to Ir-Os-Ru-Rh-Pt-Pd-Fe alloys. Polycomponent homogeneous solid solutions, which composition gradually changes from Ru-Rh-Ir-Os minerals to Fe-Pt alloys, are known in the Witwatersrand placers. A similar series of solid solutions of PGE is identified in the placers of the Guli massif on the Siberian platform. Unlike the placers of the Witwatersrand and Guli massif, where PGM are mainly represented by Os-Ir alloys, Inagli minerals have mainly a Pt-Ir-Fe composition with a low proportion of Os. The structures of most natural polyphase PGM aggregates are similar to those of artificial alloys, therefore, the former are also products of crystallization of multicomponent metal melts and their subsequent solid-phase transformations. The limits of solubility between PGE differ significantly, therefore, depending on the initial composition of metal alloys, both polycomponent solid solutions and polymineral aggregates can be formed. Based on the analysis of combined double and triple diagrams of PGE systems, the author considers possible ways of evolution of phase transformations of alloys of different composition.

Weakening of sulfate removal by aquatic plants in iron-based constructed wetlands: The rhizosphere is a sink or source of sulfur?

The fate of sulfur (S) was controlled by a complex interaction of abiotic and microbial reactions in constructed wetlands (CWs). Although zero-valent iron (ZVI) was generally considered to promote nitrogen (N) and S cycle by providing electrons, but its binding effect on sulfate (SO42−-S) removal with the rhizosphere oscillating redox conditions had not been determined. This study found that the presence of plants increased SO42−_S removal in Con-CW, while decreased it by 3.93 % in ZVI-CW accompanied by the decrease of S content in the rhizosphere substrates. The enrichment of S oxidation genes (soxA/Y and yedZ), organic S decomposition genes (aslA) and plants radial oxygen loss (ROL) accelerated the transformation of solid-phase S to SO42−-S, resulting in ZVI-CW turn from S sink to S source. Overall, the source-sink transformation provided a theoretical guidance for comprehending S cycling in CWs.

Performance activation mechanism of aluminum-based layered double hydroxides adsorbents for recovering Li+ by pH modulating

Aluminum-based adsorbents, simply prepared by eluting the lithium-aluminum layered double hydroxide precursors with deionized water, is the only industrialized adsorbents for selectively separating Li+ from saline brines. Taking the roles of lattice and surface Li+ active sites on its performances into consideration, influence of ending pH modulating on prominently improving the adsorbing capacity and stability of aluminum-based adsorbents prepared by precipitation method is initially investigated. As experimentally evidenced that, the maximum desorption amount of Li+ at the eluting stage should be controlled to around 20 mg/g Li+ rather than thoroughly removed to effectively avoid the topotactic solid-phase transformation from adsorbent to α-Al(OH)3. As-prepared adsorbents not only has high adsorption capacity up to 8.4 mg/g in 400 ppm LiCl solution, but also owns unique self-healing ability, thus promising the excellent cycling stability. It is firstly proposed that the formation of the layer-structured precursor by precipitation method is well in accordance with the three-step formation mechanism and pH modulating mainly contributes to the anions exchange between solution Cl- and interlayer OH–. This study experimentally proves the importance of pH adjusting for preparing high performance lithium adsorbents by precipitation method, which is very significant and important for effectively extracting lithium resources from the complicated multi-component liquid minerals.

Directional heat treatment technique to prepare columnar grains in a TiAl alloy: Microstructure evolution and deformation behavior

Directional TiAl alloys show excellent comprehensive mechanical properties at high temperature (HT), and their notable attributes in high-temperature deformation resistance offer them promising application potential as structural materials in the aero engine industry. Directional heat treatment (DHT) is an effective local solid phase transformation technology in alloy processing and microstructure control. The directional Ti47Al2Nb2Cr alloys with columnar grains microstructure were fabricated via multiple DHT technology, where the HT deformation performance and corresponding deformation mechanism were both investigated. Results show that both the length in axial and width in radial are increasing with the increase of DHT time, together with the reduce of columnar grains amount, ultra-large columnar grains of 58.6 mm in length and 4.8 mm in width are even obtained, which makes it possible to realize the directional single crystals fabrication further, and the DHT-TiAl alloy may possess a tensile strength of 611.7 MPa at 800 ℃. For the first time, the mechanism of columnar grain growth is considered from the point of thermodynamics via analyzing the driving force of different DHT regions, which is thought to be greatly related to the temperature gradient, and the rule of preferred orientation choosing for columnar grains growth is discussed as well, then we defined the possible conditions of controlling columnar grains steady growth. Eventually, the detailed deformation mechanism of the multiple-DHT treated TiAl alloy was analyzed by transmission electron microscopy (TEM), which demonstrates that the twin intersections together with stress-induced γ variants within γ matrix, and the well-known long period stacking order (LPSO) structure 6 R and 9 R characterized by periodic stacking fault both found near α2 phase and γ twins/pseudo-twins further improved the plastic deformation accommodation and interface compatibility of DHT-TiAl alloy. This observed microstructure transformation and corresponding mechanical performance improvement demonstrate the potential of DHT technology in microstructure improving and properties strengthening for TiAl alloys during practical manufacturing process.

Effect of multi wall carbon nanotubes during semi-solid to solid phase transformation in eutectic Al-Si alloy

The study explores numerically the combined effect of the base metal pouring temperature and MWCNT (multi wall carbon nanotubes) during semi-solid to solid solidification of Al-Si-MWCNT composite material. The semi-solid to solid solidification actually differs significantly both qualitatively and quantitatively from the liquid to solid solidification. During solidification of Al-Si-MWCNT composite material, the melt temperature and the cooling rate play crucial roles in the phase transformations. During liquid to solid solidification, the MWCNT significantly affects the cooling rate, leading to multiple recalescence phenomena, and influences the formation and evolution of the columnar and globular grains. Under the same condition, the MWCNT also impacts the silicon segregation, causing fluctuations in the silicon phases and its redistribution. However, during the semi-solid to solid solidification, it is observed that by decreasing the melt temperature into a semi-solid state, the segregation rate of silicon decreases which enhances more homogeneous CNT distribution. It also increases the globular volume fraction and dominates the columnar growth. Overall, the future trend of semi-solid to solid solidification of Al-Si-MWCNT composite materials lies in optimizing their properties for specific applications, expanding their use across diverse industries, and promoting sustainable manufacturing practices.

Structural pathway for nucleation and growth of topologically close-packed phase from parent hexagonal crystal

The solid diffusive phase transformation involving the nucleation and growth of new phase particles is universal and frequently employed but has not yet been fully understood at the atomic level. Here, our first-principles calculations reveal a structural formation pathway of a series of topologically close-packed (TCP) phases within the hexagonally close-packed (hcp) matrix. The results show that the nucleation follows a nonclassical nucleation process, and apart from atomic diffusion, the entire hcp→TCP transformation only involves shuffle-based displacements, with a specific 3-layer unstable hcp-ordering serving as the basic structural transformation unit (BSTU). The thickening of plate-like TCP phases relies on the formation of these unstable hcp-orderings at their coherent TCP/matrix interface to nucleate a ledge, but the ledge lacks the dislocation characteristics which is commonly considered in the conventional view. Additionally, the atomic structure of the critical nucleus for the Mg2Ca and MgZn2 Laves phases was predicted in terms of Classical Nucleation Theory (CNT). The formation of polytypes and off-stoichiometry in TCP precipitates is found to be related to the nonclassical nucleation behavior. These insights contribute to a deeper understanding of solid diffusive phase transformations at the atomic level and provide a foundation for investigating other technologically significant transformations.

Effects of microalloying and magnetic annealing on microstructures and properties of magnetic immiscible copper matrix alloys

The magnetic immiscible copper matrix alloys are extensively industrial applications due to their comprehensive properties such as high strength, high conductivity, high thermal conductivity and excellent magnetic permeability. Here, we investigated the effects of the addition of Co and Al elements on the microstructural evolution of magnetic Cu–Fe alloys (CFAs) and comprehensive properties after annealing under the static magnetic field (SMF). The results show that the microalloying was effective in enhancing the mechanical and magnetic properties but negative for the electric conductivity. The addition of Co element significantly suppressed the grains recrystallization of CFAs during the annealing process and improved the thermal stability of CFAs. Al elements homogeneously dispersed in the sample. SMF facilitated the nucleation and precipitation processes of the secondary precipitated particles in the Cu-rich matrix through the introducing the extra magnetic Gibbs free energy and also promoted the structural transformation of the secondary precipitated particles from FCC to BCC. This work indicates that SMF can be effectively used to modify the magnetic materials with exceptional comprehensive properties during the solid state phase transformation process. It also provides valuable guidance for the development of novel materials with superior comprehensive performance.

Numerical Simulation of Temperature Evolution, Solid Phase Transformation, and Residual Stress Distribution during Multi-Pass Welding Process of EH36 Marine Steel

Numerical Simulation of Temperature Evolution, Solid Phase Transformation, and Residual Stress Distribution during Multi-Pass Welding Process of EH36 Marine Steel

In-situ texturing hollow carbon host anchored with Fe single atoms accelerating solid-phase redox for Li-Se batteries

Se-based cathodes have caught tremendous attention owing to their comparable volumetric capacity and better electronic conductivity to S cathodes. However, its low utilization ratio and sluggish redox kinetics due to the high reaction barrier of solid-phase transformation from Se to Li2Se limit its practical application. Herein, an in-situ texturing hollow carbon host by gas–solid interface reaction anchored with Fe single-atomic catalyst is designed and prepared for advanced Li-Se batteries. This Se host presents high pore volume of 1.49 cm3 g−1, Fe single atom content of 1.53 wt%, and its specific structure protects single-atomic catalyst from the destructive reaction environment, thus balancing catalytic activity and durability. After Se loading by reduction of H2SeO3, this homogenous Se-based cathode delivers a superior rate capacity of 431.3 mA h g−1 at 4C, and great discharge capacity of 301.8 mA h g−1 after 1000 cycles at 10C, with high Li-ion diffusion coefficient and capacitance-contributed ratio. The distribution of relaxation times analysis verifies solid-phase transformation mechanism of this cathode and density functional theory calculations confirm the adsorption and bidirectionally catalysis effect of Fe single-atomic catalyst. This work provides a new strategy to prepare high-efficient Se cathode associated with non-noble metal single atoms for high-performance Li-Se batteries.

Multiwall carbon nanotube-hyperbranched polymaleimide core–shell nanowires with hierarchical porous and polar structure as sulfur host for sustainable lithium-sulfur batteries

Lithium–sulfur (Li–S) batteries have gained considerable attention as a promising alternative to current advanced batteries because of their low cost, natural abundance, high energy density, and environmental benignity of sulfur. The commercial application of Li–S batteries is being seriously impeded by the shuttle effect of lithium polysulfides (LiPSs) and the sluggish reaction kinetics of solid phase transformation. Herein, a novel composite material (PPI@MWCNT-Y) with a hierarchical porous skeleton and polar channel is prepared as a sulfur host using a convenient in-situ one-pot polymerization. PPI@MWCNT-Y is composed of conductive mesoporous multi-wall carbon nanotubes (MWCNTs) core and a microporous hyperbranched polymaleimide (PPI) shell formed by the self-polymerization of N,N′-1,4-phenylenedimaleimide (PDM). The mesoporous and conductive channels in PPI@MWCNT-Y improve the redox kinetics of the active materials by serving as a fast electron and Li-ions transportation pathway. The microporous structure and abundant adsorption sites (N and O atoms) within the PPI@MWCNT-Y served as physical and chemical barriers, preventing the loss of LiPSs, and suppressing the shuttle effect. Consequently, the S/PPI@MWCNT-38 composite exhibited a high discharge capacity of 1338 mAh g−1 at 0.2 C and a low-capacity decay rate of 0.088% for 400 cycles at 1 C.