Enhancing P2/O3 Biphasic Cathode Performance for Sodium-Ion Batteries: A Metaheuristic Approach to Multi-Element Doping Design.

Sodium-ion batteries (SIBs) have emerged as a compelling alternative to lithium-ion batteries (LIBs), exhibiting comparable electrochemical performance while capitalizing on the abundant availability of sodium resources. In SIBs, P2/O3 biphasic cathodes, despite their high energy, require furthur improvements in stability to meet current energy demands. This study introduces a systematic methodology that leverages the meta-heuristically assisted NSGA-II algorithm to optimize multi-element doping in electrode materials, aiming to transcend conventional trial-and-error methods and enhance cathode capacity by the synergistic integration of P2 and O3 phases. A comprehensive phase analysis of the meta-heuristically designed cathode material Na0.76Ni0.20Mn0.42Fe0.30Mg0.04Ti0.015Zr0.025O2 (D-NFMO) is presented, showcasing its remarkable initial reversible capacity of 175.5 mAh g-1 and exceptional long-term cyclic stability in sodium cells. The investigation of structural composition and the stabilizing mechanisms is performed through the integration of multiple characterization techniques. Remarkably, the irreversible phase transition of P2→OP4 in D-NFMO is observed to be dramatically suppressed, leading to a substantial enhancement in cycling stability. The comparison with the pristine cathode (P-NFMO) offers profound insights into the long-term electrochemical stability of D-NFMO, highlighting its potential as a high-voltage cathode material utilizing abundant earth elements in SIBs. This study opens up new possibilities for future advancements in sodium-ion battery technology.

Nanocrystalline Composite Layer Realized by Simple Sintering Without Surface Treatment, Reducing Hydrophilicity and Increasing Thermal Conductivity.

The surface treatment for a polymer-ceramic composite is additionally performed in advanced material industries. To prepare the composite without a surface treatment, the simplest way to manufacture an advanced ceramic-particle is devised. The method is the formation of a nanocrystalline composite layer through the simple liquid-phase sintering. Using magnesia (MgO) which shows hydrophilicity, a nanocrystalline surface layer is realized by liquid-phase sintering. The amorphous matrix of nanocrystalline composite layer makes MgO hydrophobic and ensures miscibility with polymers, and the nanocrystalline MgO ensures high thermal conductivity. In addition, the liquid phase removes the open pores and makes the surface morphology smooth MgO with smooth surface (MgO-SM). Thermal interface materials (TIM) prepared with MgO-SM and epoxy show a high thermal conductivity of ≈7.5 W m-1 K-1 , which is significantly higher than 4.5 W m-1 K-1 of pure MgO TIM. Consequently, the formation process of a nanocrystalline surface layer utilizing simple liquid-phase sintering is proposed as a fabrication method for a next-generation ceramic-filler. In addition, it is fundamentally identified that the thermal conductivity of MgO depends on the Mg deficiency, and therefore a poly-crystal MgO-SM (produced at a low temperature) has a higher thermal conductivity than a single-crystal MgO (produced at a high temperature).

Na2ZrFe(PO4)3─A Rhombohedral NASICON-Structured Material: Synthesis, Structure and Na-Intercalation Behavior.

A NASICON-structured earth-abundant mixed transition metal (TM) containing Na-TM-phosphate, viz., Na2ZrFe(PO4)3, has been prepared via a sol-gel route using a low-cost Fe3+-based precursor. The as-prepared material crystallizes in the desired rhombohedral NASICON structure (space group: R3̅c) at room temperature. Synchrotron X-ray diffraction (XRD), transmission electron microscopy, X-ray absorption spectroscopy, etc., have been performed to determine the crystal structure, associated details, composition, and electronic structures. In light of the structural features, as one of the possible functionalities of Na2FeZr(PO4)3, Na-intercalation/deintercalation has been examined, which indicates the occurrence of reversible electrochemical Na-insertion/extraction via Fe2+/Fe3+ redox at an average potential of ∼2.5 V. The electrochemical data and direct evidences from operando synchrotron XRD indicate that the rhombohedral structure is preserved during Na-insertion/extraction, albeit within a certain range of Na-content (i.e., ∼2-3 p.f.u.), beyond which rhombohedral → monoclinic transformation takes place. Within this range, Na-insertion/extraction takes place via solid-solution pathway, resulting in outstanding cyclic stability, higher Na-diffusivity, and good rate-capability. To the best of the authors' knowledge, this represents the first in-depth structural, compositional, and electrochemical studies with Na2ZrFe(PO4)3, along with the interplay between those, which provide insights into the design of similar low-cost materials for various applications, including sustainable electrochemical energy storage systems.

Unprecedented Cyclability and Moisture Durability of NaCrO2 Sodium-Ion Battery Cathode via Simultaneous Al Doping and Cr2O3 Coating.

Although there are many cathode candidates for sodium-ion batteries (NIBs), NaCrO2 remains one of the most attractive materials due to its reasonable level of capacity, nearly flat reversible voltages, and high thermal stability. However, the cyclic stability of NaCrO2 needs to be further improved in order to compete with other state-of-the-art NIB cathodes. In this study, we show that Cr2O3-coated and Al-doped NaCrO2, which is synthesized through a simple one-pot synthesis, can achieve unprecedented cyclic stability. We confirm the preferential formation of a Cr2O3 shell and a Na(Cr1-2xAl2x)O2 core, rather than xAl2O3/NaCrO2 or Na1/1+2x(Cr1/1+2xAl2x/1+2x)O2, through spectroscopic and microscopic methods. The core/shell compounds exhibit superior electrochemical properties compared to either Cr2O3-coated NaCrO2 without Al dopants or Al-doped NaCrO2 without shells because of their synergistic contributions. As a result, Na(Cr0.98Al0.02)O2 with a thin Cr2O3 layer (5 nm) shows no capacity fading during 1000 charge/discharge cycles while maintaining the rate capability of pristine NaCrO2. In addition, the compound is inert against humid air and water. We also discuss the reasons for the excellent performance of Cr2O3-coated Na(Cr1-2xAl2x)O2.

Synchrotron radiation based X-ray techniques for analysis of cathodes in Li rechargeable batteries.

Li-ion rechargeable batteries are promising systems for large-scale energy storage solutions. Understanding the electrochemical process in the cathodes of these batteries using suitable techniques is one of the crucial steps for developing them as next-generation energy storage devices. Due to the broad energy range, synchrotron X-ray techniques provide a better option for characterizing the cathodes compared to the conventional laboratory-scale characterization instruments. This work gives an overview of various synchrotron radiation techniques for analyzing cathodes of Li-rechargeable batteries by depicting instrumental details of X-ray diffraction, X-ray absorption spectroscopy, X-ray imaging, and X-ray near-edge fine structure-imaging. Analysis and simulation procedures to get appropriate information of structural order, local electronic/atomic structure, chemical phase mapping and pores in cathodes are discussed by taking examples of various cathode materials. Applications of these synchrotron techniques are also explored to investigate oxidation state, metal-oxygen hybridization, quantitative local atomic structure, Ni oxidation phase and pore distribution in Ni-rich layered oxide cathodes.

Optimal Composition of Li Argyrodite with Harmonious Conductivity and Chemical/Electrochemical Stability: Fine-Tuned Via Tandem Particle Swarm Optimization.

A tandem (two-step) particle swarm optimization (PSO) algorithm is implemented in the argyrodite-based multidimensional composition space for the discovery of an optimal argyrodite composition, i.e., with the highest ionic conductivity (7.78 mS cm-1 ). To enhance the industrial adaptability, an elaborate pellet preparation procedure is not used. The optimal composition (Li5.5 PS4.5 Cl0.89 Br0.61 ) is fine-tuned to enhance its practical viability by incorporating oxygen in a stepwise manner. The final composition (Li5.5 PS4.23 O0.27 Cl0.89 Br0.61 ), which exhibits an ionic conductivity (σion ) of 6.70 mS cm-1 and an activation barrier of 0.27 eV, is further characterized by analyzing both its moisture and electrochemical stability. Relative to the other compositions, the exposure of Li5.5 PS4.23 O0.27 Cl0.89 Br0.61 to a humid atmosphere results in the least amount of H2 S released and a negligible change in structure. The improvement in the interfacial stability between the Li(Ni0.9 Co0.05 Mn0.05 )O2 cathode and Li5.5 PS4.23 O0.27 Cl0.89 Br0.61 also results in greater specific capacity during fast charge/discharge. The structural and chemical features of Li5.5 PS4.5 Cl0.89 Br0.61 and Li5.5 PS4.23 O0.27 Cl0.89 Br0.61 argyrodites are characterized using synchrotron X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. This work presents a novel argyrodite composition with favorably balanced properties while providing broad insights into material discovery methodologies with applications for battery development.

Unravelling the Nature of the Intrinsic Complex Structure of Binary-Phase Na-Layered Oxides.

The layered sodium transition metal oxide, NaTMO2 (TM = transition metal), with a binary or ternary phases has displayed outstanding electrochemical performance as a new class of strategy cathode materials for sodium-ion batteries (SIBs). Herein, an in-depth phase analysis of developed Na1-x TMO2 cathode materials, Na0.76 Ni0.20 Fe0.40 Mn0.40 O2 with P2- and O3-type phases (NFMO-P2/O3) is offered. Structural visualization on an atomic scale is also provided and the following findings are unveiled: i) the existence of a mixed-phase intergrowth layer distribution and unequal distribution of P2 and O3 phases along two different crystal plane indices and ii) a complete reversible charge/discharge process for the initial two cycles that displays a simple phase transformation, which is unprecedented. Moreover, first-principles calculations support the evidence of the formation of a binary NFMO-P2/O3 compound, over the proposed hypothetical monophasic structures (O3, P3, O'3, and P2 phases). As a result, the synergetic effect of the simultaneous existence of P- and O-type phases with their unique structures allows an extraordinary level of capacity retention in a wide range of voltage (1.5-4.5 V). It is believed that the insightful understanding of the proposed materials can introduce new perspectives for the development of high-voltage cathode materials for SIBs.

Mn-Dopant Differentiating the Ru and Ir Oxidation States in Catalytic Oxides Toward Durable Oxygen Evolution Reaction in Acidic Electrolyte.

Designing an efficient and durable electrocatalyst for the sluggish oxygen evolution reaction (OER) at the anode remains the foremost challenge in developing proton exchange membrane (PEM) electrolyzers. Here, a highly active and durable cactus-like nanoparticle with an exposed heterointerface between the IrO2 and the low oxidation state Ru by introducing a trace amount of Mn dopant is reported. The heterostructure fabrication relies on initial mixing of the Ru and Ir phases before electrochemical oxidation to produce a conjoined Ru/IrO2 heterointerface. Benefitting from electron transfer at the heterointerface, the low oxidation state Ru species shows excellent initial activity, which is maintained even after 180 h of continuous OER test. In a half-cell test, the Mn-doped RuIr nanocactus (Mn-RuIr NCT) achieves a mass activity of 1.85 A mgIr+Ru -1 at 1.48 VRHE , which is 139-fold higher than that of commercial IrO2 . Moreover, the superior electrocatalytic performance of Mn-RuIr NCT in the PEM electrolysis system ensures its viability in practical uses. The results of the excellent catalytic performance for acidic OER indicate that the heterostructuring robust rutile IrO2 and the highly active Ru species with a low oxidation state on the catalyst surface drive a synergistic effect.

Oxygen-Vacancy-Driven Orbital Reconstruction at the Surface of TiO2 Core-Shell Nanostructures.

Oxygen vacancies and their correlation with the electronic structure are crucial to understanding the functionality of TiO2 nanocrystals in material design applications. Here, we report spectroscopic investigations of the electronic structure of anatase TiO2 nanocrystals by employing hard and soft X-ray absorption spectroscopy measurements along with the corresponding model calculations. We show that the oxygen vacancies significantly transform the Ti local symmetry by modulating the covalency of titanium-oxygen bonds. Our results suggest that the altered Ti local symmetry is similar to the C3v, which implies that the Ti exists in two local symmetries (D2d and C3v) at the surface. The findings also indicate that the Ti distortion is a short-range order effect and presumably confined up to the second nearest neighbors. Such distortions modulate the electronic structure and provide a promising approach to structural design of the TiO2 nanocrystals.

Soft X-ray Absorption Spectroscopic Investigation of Li(Ni0.8Co0.1Mn0.1)O2 Cathode Materials.

Herein, we report the soft X-ray absorption spectroscopic investigation for Li(Ni0.8Co0.1Mn0.1)O2 cathode material during charging and discharging. These measurements were carried out at the Mn L-, Co L-, and Ni L-edges during various stages of charging and discharging. Both the Mn and Co L-edge spectroscopic measurements reflect the invariance in the oxidation states of Mn and Co ions. The Ni L-edge measurements show the modification of the oxidation state of Ni ions during the charging and discharging process. These studies show that eg states are affected dominantly in the case of Ni ions during the charging and discharging process. The O K-edge measurements reflect modulation of metal-oxygen hybridization as envisaged from the area-ratio variation of spectral features corresponding to t2g and eg states.

Graphite as a Long-Life Ca2+-Intercalation Anode and its Implementation for Rocking-Chair Type Calcium-Ion Batteries.

Herein, graphite is proposed as a reliable Ca2+-intercalation anode in tetraglyme (G4). When charged (reduced), graphite accommodates solvated Ca2+-ions (Ca-G4) and delivers a reversible capacity of 62 mAh g-1 that signifies the formation of a ternary intercalation compound, Ca-G4·C72. Mass/volume changes during Ca-G4 intercalation and the evolution of in operando X-ray diffraction studies both suggest that Ca-G4 intercalation results in the formation of an intermediate phase between stage-III and stage-II with a gallery height of 11.41 Å. Density functional theory calculations also reveal that the most stable conformation of Ca-G4 has a planar structure with Ca2+ surrounded by G4, which eventually forms a double stack that aligns with graphene layers after intercalation. Despite large dimensional changes during charge/discharge (C/D), both rate performance and cyclic stability are excellent. Graphite retains a substantial capacity at high C/D rates (e.g., 47 mAh g-1 at 1.0 A g-1 s vs 62 mAh g-1 at 0.05 A g-1) and shows no capacity decay during as many as 2000 C/D cycles. As the first Ca2+-shuttling calcium-ion batteries with a graphite anode, a full-cell is constructed by coupling with an organic cathode and its electrochemical performance is presented.

KCrS2 Cathode with Considerable Cyclability and High Rate Performance: The First K+ Stoichiometric Layered Compound for Potassium-Ion Batteries.

KCrS2 is presented as a stable and high-rate layered material that can be used as a cathode in potassium-ion batteries. As far as it is known, KCrS2 is the only layered material with stoichiometric amounts of K+ , which enables coupling with a graphite anode for full-cell construction. Cr(III)/Cr(IV) redox in KCrS2 is also unique, because LiCrS2 and NaCrS2 are known to experience S2- /S2 2- redox. O3-KCrS2 is first charged to P3-K0.39 CrS2 and subsequently discharged to O'3-K0.8 CrS2 , delivering an initial discharge capacity of 71 mAh g-1 . The following charge/discharge (C/D) shows excellent reversibility between O'3-K0.8 CrS2 and P3-K0.39 CrS2 , retaining ≈90% of the initial capacity during 1000 continuous cycles. The rate performance is also noteworthy. A C/D rate increase of 100-fold (0.05 to 5 C) reduces the reversible capacity only by 39% (71 to 43 mAh g-1 ). The excellent cyclic stability and high rate performance are ascribed to the soft sulfide framework, which can effectively buffer the stress caused by K+ deinsertion/insertion. During the transformation between P3-K0.39 CrS2 and O'3-K0.8 CrS2 , the material resides mostly in the P3 phase, which minimizes the abrupt dimension change and allows facile K+ diffusion through spacious prismatic sites. Structural analysis and density functional theory calculations firmly support this reasoning.

High-resolution patterning of solution-processable materials via externally engineered pinning of capillary bridges.

Electronics based on solution-processable materials are promising for applications in many fields which stimulated enormous research interest in liquid-drying and pattern formation. However, assembling of structure with submicrometre/nanometre resolution through liquid process is very challenging. We show a simple method to rapidly generate polymer structures with deep-submicrometre-sized features over large areas. In this method, a solution film is dried on a substrate under a suspended flexible template with groove/ridge surface topography. Upon solvent evaporation, the solution splits in the grooves and forms capillary bridges between the template and substrate, which are firmly pinned by the edges of the template grooves. This groove pinning stabilizes the contact lines, thereby allowing the formation of fine patterned structures with high aspect ratios which were used to fabricate various functional materials and electronic devices. We also produced secondary self-assembled nano-stripe patterns with resolutions of about 50 nm on the primary lines.

Unraveling the Magnesium-Ion Intercalation Mechanism in Vanadium Pentoxide in a Wet Organic Electrolyte by Structural Determination.

Magnesium batteries have received attention as a type of post-lithium-ion battery because of their potential advantages in cost and capacity. Among the host candidates for magnesium batteries, orthorhombic α-V2O5 is one of the most studied materials, and it shows a reversible magnesium intercalation with a high capacity especially in a wet organic electrolyte. Studies by several groups during the last two decades have demonstrated that water plays some important roles in getting higher capacity. Very recently, proton intercalation was evidenced mainly using nuclear resonance spectroscopy. Nonetheless, the chemical species inserted into the host structure during the reduction reaction are still unclear (i.e., Mg(H2O)n2+, Mg(solvent, H2O)n2+, H+, H3O+, H2O, or any combination of these). To characterize the intercalated phase, the crystal structure of the magnesium-inserted phase of α-V2O5, electrochemically reduced in 0.5 M Mg(ClO4)2 + 2.0 M H2O in acetonitrile, was solved for the first time by the ab initio method using powder synchrotron X-ray diffraction data. The structure was tripled along the b-axis from that of the pristine V2O5 structure. No appreciable densities of elements were observed other than vanadium and oxygen atoms in the electron density maps, suggesting that the inserted species have very low occupancies in the three large cavity sites of the structure. Examination of the interatomic distances around the cavity sites suggested that H2O, H3O+, or solvated magnesium ions are too big for the cavities, leading us to confirm that the intercalated species are single Mg2+ ions or protons. The general formula of magnesium-inserted V2O5 is Mg0.17HxV2O5, (0.66 ≤ x ≤ 1.16). Finally, density functional theory calculations were carried out to locate the most plausible atomic sites of the magnesium and protons, enabling us to complete the structure modeling. This work provides an explicit answer to the question about Mg intercalation into α-V2O5.

Iron Oxide Photoelectrode with Multidimensional Architecture for Highly Efficient Photoelectrochemical Water Splitting.

Nanostructured metal oxide semiconductors have shown outstanding performances in photoelectrochemical (PEC) water splitting, but limitations in light harvesting and charge collection have necessitated further advances in photoelectrode design. Herein, we propose anodized Fe foams (AFFs) with multidimensional nano/micro-architectures as a highly efficient photoelectrode for PEC water splitting. Fe foams fabricated by freeze-casting and sintering were electrochemically anodized and directly used as photoanodes. We verified the superiority of our design concept by achieving an unprecedented photocurrent density in PEC water splitting over 5 mA cm-2 before the dark current onset, which originated from the large surface area and low electrical resistance of the AFFs. A photocurrent of over 6.8 mA cm-2 and an accordingly high incident photon-to-current efficiency of over 50 % at 400 nm were achieved with incorporation of Co oxygen evolution catalysts. In addition, research opportunities for further advances by structual and compositional modifications are discussed, which can resolve the low fill factoring behavior and improve the overall performance.

Red green blue emissive lead sulfide quantum dots: heterogeneous synthesis and applications.

Visible emission colloidal quantum dots (QDs) have shown promise in optical and optoelectronic applications. These QDs are typically composed of relatively expensive elements in the form of indium, cadmium, and gallium since alternative candidate materials exhibiting similar properties are yet to be realized. Herein, for the first time, we report red green blue (RGB) photoluminescences with quantum yields of 18% from earth-abundant lead sulfide (PbS) QDs. The visible emissive property is mainly attributed to a high degree of crystallinity even for the extremely small QD sizes (1-3 nm), which is realized by employing a heterogeneous reaction methodology at high growth temperatures (>170 °C). We demonstrate that the proposed heterogeneous synthetic method can be extended to the synthesis of other metal chalcogenide QDs, such as zinc sulfide and zinc selenide, which are promising for future industrial applications. More importantly, benefiting from the enlarged band gaps, the as-prepared PbS solar cells show an impressive open circuit voltage (∼0.8 V) beyond that reported to date.

Inhibition of methane and natural gas hydrate formation by altering the structure of water with amino acids.

Natural gas hydrates are solid hydrogen-bonded water crystals containing small molecular gases. The amount of natural gas stored as hydrates in permafrost and ocean sediments is twice that of all other fossil fuels combined. However, hydrate blockages also hinder oil/gas pipeline transportation, and, despite their huge potential as energy sources, our insufficient understanding of hydrates has limited their extraction. Here, we report how the presence of amino acids in water induces changes in its structure and thus interrupts the formation of methane and natural gas hydrates. The perturbation of the structure of water by amino acids and the resulting selective inhibition of hydrate cage formation were observed directly. A strong correlation was found between the inhibition efficiencies of amino acids and their physicochemical properties, which demonstrates the importance of their direct interactions with water and the resulting dissolution environment. The inhibition of methane and natural gas hydrate formation by amino acids has the potential to be highly beneficial in practical applications such as hydrate exploitation, oil/gas transportation, and flow assurance. Further, the interactions between amino acids and water are essential to the equilibria and dynamics of many physical, chemical, biological, and environmental processes.

Effects of Ag-embedment on electronic and ionic conductivities of LiMnPO4 and its performance as a cathode for lithium-ion batteries.

An Ag-embedded LiMnPO4 (LMP) cathode was synthesized by solid-state reaction using a 1 wt% Ag precursor. Structure, morphology, and electrical conductivity studies of Ag-embedded LMP were performed by high resolution powder X-ray diffraction, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and four probe measurements. An Ag nanoparticle (∼26 nm) surrounded by several olivine crystallites within a single particle dramatically improved the overall electrical conductivity of LMP by four orders of magnitude relative to that of pristine LMP, playing roles as conducting bridges among LMP crystallites as well as particles. Rietveld analysis confirmed structural variations related to the modification of atomic bond lengths of Mn-O, P-O, and Li-O coordination due to Ag-embedment and thereby leads to facile Li ion diffusion in LMP. Consequently, although a small amount of Ag was included, the Ag-embedded LMP cathode exhibited outstanding electrochemical performances (92 mA h g(-1) at 10 C) versus lithium.

Gas hydrate inhibition by perturbation of liquid water structure.

Natural gas hydrates are icy crystalline materials that contain hydrocarbons, which are the primary energy source for this civilization. The abundance of naturally occurring gas hydrates leads to a growing interest in exploitation. Despite their potential as energy resources and in industrial applications, there is insufficient understanding of hydrate kinetics, which hinders the utilization of these invaluable resources. Perturbation of liquid water structure by solutes has been proposed to be a key process in hydrate inhibition, but this hypothesis remains unproven. Here, we report the direct observation of the perturbation of the liquid water structure induced by amino acids using polarized Raman spectroscopy, and its influence on gas hydrate nucleation and growth kinetics. Amino acids with hydrophilic and/or electrically charged side chains disrupted the water structure and thus provided effective hydrate inhibition. The strong correlation between the extent of perturbation by amino acids and their inhibition performance constitutes convincing evidence for the perturbation inhibition mechanism. The present findings bring the practical applications of gas hydrates significantly closer, and provide a new perspective on the freezing and melting phenomena of naturally occurring gas hydrates.

Thermoelectric properties and chlorine doping effect of In4Pb0.01Sn0.03Se2.9Clx polycrystalline compounds.

We investigated the thermoelectric properties of Cl-doped polycrystalline compounds In4Pb0.01Sn0.03Se2.9Clx (x = 0.02, 0.04, and 0.06). X-ray diffraction measurement shows a gradual change in lattice volume for x ≤ 0.04 without any impurity phases indicating a systemic change in Cl doping. The Cl doping in the compounds has the effect of increasing carrier concentration and the effective mass of carriers, resulting in an increase in power factor at a high temperature (∼700 K). Because of the increased electrical conductivity at a high temperature, the dimensionless thermoelectric figure of merit ZT reaches 1.25 at 723 K for the x = 0.04 Cl-doped compound, which is a relatively high value for n-type polycrystalline materials.