Unraveling the "Gap-Filling" Mechanism of Multiple Charge Carriers in Aqueous Zn-MoS2 Batteries.

The utilization rate of active sites in cathode materials for Zn-based batteries is a key factor determining the reversible capacities. However, a long-neglected issue of the strong electrostatic repulsions among divalent Zn2+ in hosts inevitably causes the squander of some active sites (i.e., gap sites). Herein, we address this conundrum by unraveling the "gap-filling" mechanism of multiple charge carriers in aqueous Zn-MoS2 batteries. The tailored MoS2 /(reduced graphene quantum dots) hybrid features an ultra-large interlayer spacing (2.34 nm), superior electrical conductivity/hydrophilicity, and robust layered structure, demonstrating highly reversible NH4 + /Zn2+ /H+ co-insertion/extraction chemistry in the 1 M ZnSO4 +0.5 M (NH4 )2 SO4 aqueous electrolyte. The NH4 + and H+ ions can act as gap fillers to fully utilize the active sites and screen electrostatic interactions to accelerate the Zn2+ diffusion. Thus, unprecedentedly high rate capability (439.5 and 104.3 mAh g-1 at 0.1 and 30 A g-1 , respectively) and ultra-long cycling life (8000 cycles) are achieved.

Low-cost BPO4 In Situ Synthetic Li3PO4 Coating and B/P-Doping to Boost 4.8 V Cyclability for Sulfide-Based All-Solid-State Lithium Batteries.

Structural damage of Ni-rich layered oxide cathodes such as LiNi0.8Co0.1Mn0.1O2 (NCM811) and serious interfacial side reactions and physical contact failures with sulfide electrolytes (SEs) are the main obstacles restricting ≥4.6 V high-voltage cyclability of all-solid-state lithium batteries (ASSLBs). To tackle this constraint, here, a modified NCM811 with Li3PO4 coating and B/P co-doping using inexpensive BPO4 as raw materials via the one-step in situ synthesis process is presented. Phosphates have good electrochemical stability and contain the same anion (O2-) and cation (P5+) as in cathode and SEs, respectively, thus Li3PO4 coating precludes interfacial anion exchange, lessening side reactivity. Based on the high bond energy of B─O and P─O, the lattice O and crystal texture of NCM811 can be stabilized by B3+/P5+ co-doping, thereby suppressing microcracks during high-voltage cycling. Therefore, when tested in combination with Li─In anode and Li6PS5Cl solid electrolytes (LPSCl), the modified NCM811 exhibits extraordinary performance, with 200.36 mAh g-1 initial discharge capacity (4.6 V), cycling 2300 cycles with decay rate as low as 0.01% per cycle (1C), and 208.26 mAh g-1 initial discharge capacity (4.8 V), cycling 1986 cycles with 0.02% per cycle decay rate. Simultaneously, it also has remarkable electrochemical abilities at both -20 °C and 60 °C.

Boosting the Reversibility and Kinetics of Anionic Redox Chemistry in Sodium-Ion Oxide Cathodes via Reductive Coupling Mechanism.

Activating anionic redox chemistry in layered oxide cathodes is a paradigmatic approach to devise high-energy sodium-ion batteries. Unfortunately, excessive oxygen redox usually induces irreversible lattice oxygen loss and cation migration, resulting in rapid capacity and voltage fading and sluggish reaction kinetics. Herein, the reductive coupling mechanism (RCM) of uncommon electron transfer from oxygen to copper ions is unraveled in a novel P2-Na0.8Cu0.22Li0.08Mn0.67O2 cathode for boosting the reversibility and kinetics of anionic redox reactions. The resultant strong covalent Cu-(O-O) bonding can efficaciously suppress excessive oxygen oxidation and irreversible cation migration. Consequently, the P2-Na0.8Cu0.22Li0.08Mn0.67O2 cathode delivers a marvelous rate capability (134.1 and 63.2 mAh g-1 at 0.1C and 100C, respectively) and outstanding long-term cycling stability (82% capacity retention after 500 cycles at 10C). The intrinsic functioning mechanisms of RCM are fully understood through systematic in situ/ex situ characterizations and theoretical computations. This study opens a new avenue toward enhancing the stability and dynamics of oxygen redox chemistry.

The Effect of Annealing on the Soft Magnetic Properties and Microstructure of Fe82Si2B13P1C3 Amorphous Iron Cores.

This research paper investigated the impact of normal annealing (NA) and magnetic field annealing (FA) on the soft magnetic properties and microstructure of Fe82Si2B13P1C3 amorphous alloy iron cores. The annealing process involved various methods of magnetic field application: transverse magnetic field annealing (TFA), longitudinal magnetic field annealing (LFA), transverse magnetic field annealing followed by longitudinal magnetic field annealing (TLFA) and longitudinal magnetic field annealing followed by transverse magnetic field annealing (LTFA). The annealed samples were subjected to testing and analysis using techniques such as differential scanning calorimetry (DSC), transmission electron microscopy (TEM), X-ray diffraction (XRD), magnetic performance testing equipment and magneto-optical Kerr microscopy. The obtained results were then compared with those of commercially produced Fe80Si9B11. Fe82Si2B13P1C3 demonstrated the lowest loss of P1.4T,2kHz = 8.1 W/kg when annealed in a transverse magnetic field at 370 °C, which was 17% lower than that of Fe80Si9B11. When influenced by the longitudinal magnetic field, the magnetization curve tended to become more rectangular, and the coercivity (B3500A/m) of Fe82Si2B13P1C3 reached 1.6 T, which was 0.05 T higher than that of Fe80Si9B11. During the 370 °C annealing process of the Fe82Si2B13P1C3 amorphous iron core, the internal stress in the strip gradually dissipated, and impurity domains such as fingerprint domains disappeared and aligned with the length direction of the strip. Consequently, wide strip domains with low resistance and easy magnetization were formed, thereby reducing the overall loss of the amorphous iron core.

Facet Engineering and Pore Design Boost Dynamic Fe Exchange in Oxygen Evolution Catalysis to Break the Activity-Stability Trade-Off.

The oxygen evolution reaction (OER) plays a vital role in renewable energy technologies, including in fuel cells, metal-air batteries, and water splitting; however, the currently available catalysts still suffer from unsatisfactory performance due to the sluggish OER kinetics. Herein, we developed a new catalyst with high efficiency in which the dynamic exchange mechanism of active Fe sites in the OER was regulated by crystal plane engineering and pore structure design. High-density nanoholes were created on cobalt hydroxide as the catalyst host, and then Fe species were filled inside the nanoholes. During the OER, the dynamic Fe was selectively and strongly adsorbed by the (101̅0) sites on the nanohole walls rather than the (0001) basal plane, and at the same time the space-confining effect of the nanohole slowed down the Fe diffusion from catalyst to electrolyte. As a result, a local high-flux Fe dynamic equilibrium inside the nanoholes for OER was achieved, as demonstrated by the Fe57 isotope labeled mass spectrometry, thereby delivering a high OER activity. The catalyst showed a remarkably low overpotential of 228 mV at a current density of 10 mA cm-2, which is among the best cobalt-based catalysts reported so far. This special protection strategy for Fe also greatly improved the catalytic stability, reducing the Fe leaching amount by 2 orders of magnitude compared with the pure Fe hydroxide catalyst and thus delivering a long-term stability of 130 h. An assembled Zn-air battery was stably cycled for 170 h with a low discharge/charge voltage difference of 0.72 V.

Mo-Pre-Intercalated MnO2 Cathode with Highly Stable Layered Structure and Expanded Interlayer Spacing for Aqueous Zn-Ion Batteries.

Although manganese-based oxides possess high voltage and low cost, the sluggish reaction kinetics and poor structural stability hinder their applications in aqueous rechargeable Zn-ion batteries (ZIBs). Herein, a molybdenum (Mo) pre-intercalation strategy is proposed to solve the above issues of δ-MnO2. The pre-intercalated Mo dopants, acting as the interlayer pillars, can not only expand the interlayer spacing but also reinforce the layered structure of δ-MnO2, finally achieving enhanced reaction kinetics and superb cycling stability during carrier (de)intercalation. Moreover, oxygen defects, introduced due to Mo-pre-intercalation, play a critical role in the fast reaction kinetics and capacity improvement of the Mo-pre-intercalated δ-MnO2 (Mo-MnO2) cathode. Therefore, the Mo-MnO2 cathode displays a high energy density of 451 Wh kg-1 (based on cathode mass), excellent rate capability, and admirable long-term cycling performance with a high capacity of 159 mAhg-1 at 1.0 A g-1 after 1000 cycles. In addition, the energy storage mechanism of Zn2+/H+ stepwise reversible (de)intercalation is also revealed by ex situ experiments. This work provides an insightful guide for boosting the electrochemical performance of Mn-based oxide cathodes for ZIBs.

Powder Metallurgy Route to Ultrafine-Grained Refractory Metals.

Ultrafine-grained (UFG) refractory metals are promising materials for applications in aerospace, microelectronics, nuclear energy, and many others under extreme environments. Powder metallurgy (PM) allows to produce such materials with well-controlled chemistry and microstructure at multiple length scales and near-net shape manufacturing. However, sintering refractory metals to full density while maintaining a fine microstructure is still challenging due to the high sintering temperature and the difficulty to separate the kinetics of densification versus grain growth. Here an overview of the sintering issues, microstructural design rules, and PM practices towards UFG and nanocrystalline refractory metals are sought to be provided. The previous efforts shall be reviewed to address the processing challenges, including the use of fine/nanopowders, second-phase grain growth inhibitors, and field-assisted sintering techniques. Recently, pressureless two-step sintering has been successfully demonstrated in producing dense UFG refractory metals down to ≈300 nm average grain size with a uniform microstructure and this technological breakthrough shall be reviewed. PM progresses in specific materials systems shall be next reviewed, including elementary metals (W and Mo), refractory alloys (W-Re), refractory high-entropy alloys, and their composites. Last, future developments and the endeavor towards UFG and nanocrystalline refractory metals with exceptionally uniform microstructure and improved properties are outlined.

Investigation on the Attainment of High-Density 316L Stainless Steel with Selective Laser Sintering.

Due to the low density of the green part produced by selective laser sintering (SLS), previous reports mainly improve the sample's density through the infiltration of low-melting metals or using isostatic pressing technology. In this study, the feasibility of preparing high-density 316L stainless steel using 316L and epoxy resin E-12 as raw materials for SLS combined with debinding and sintering was investigated. The results indicated that in an argon atmosphere, high carbon and oxygen contents, along with the uneven distribution of oxygen, led to the formation of impurity phases such as metal oxides, including Cr2O3 and FeO, preventing the effective densification of the sintered samples. Hydrogen-sintered samples can achieve a high relative density exceeding 98% without losing their original design shape. This can be attributed to hydrogen's strong reducibility (effectively reducing the carbon and oxygen contents in the samples, improving their distribution uniformity, and eliminating impurity phases) and hydrogen's higher thermal conductivity (about 10 times that of argon, reducing temperature gradients in the sintered samples and promoting better sintering). The microstructure of the hydrogen-sintered samples consisted of equiaxed austenite and ferrite phases. The samples exhibited the highest values of tensile strength, yield strength, and elongation at 1440 °C, reaching 513.5 MPa, 187.4 MPa, and 76.1%, respectively.

S and O Co-Coordinated Mo Single Sites in Hierarchically Porous Tubes from Sulfur-Enamine Copolymerization for Oxygen Reduction and Evolution.

The highly efficient bifunctional catalyst for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is the key to achieving high-performance rechargeable Zn-air batteries. Non-precious-metal single-atom catalysts (SACs) have attracted intense interest due to their low cost and very high metal atomic utilization; however, high-activity bifunctional non-precious-metal SACs are still rare. Herein, we develop a new nanospace-confined sulfur-enamine copolymerization strategy to prepare a new type of bifunctional Mo SACs with O/S co-coordination (Mo-O2S2-C) supported on the multilayered, hierarchically porous hollow tubes. The as-prepared catalyst can not only expose more active sites and facilitate mass transfer due to their combined micropores, mesopores, and macropores but also have the S/O co-coordination structure for optimizing the adsorption energies of the ORR intermediates. Its ORR activity is among the highest, and it shows a low overpotential of 324 mV for the OER at 10 mA cm-2 in all of the reported Mo-based catalysts. When assembled in a Zn-air battery, it exhibits a high maximal power density of 197.3 mW cm-2 and a long service life of 50 hours, superior to those of Zn-air batteries using commercial Pt/C+IrO2.

Unveiling the "Proton Lubricant" Chemistry in Aqueous Zinc-MoS2 Batteries.

Proton insertion chemistry in aqueous zinc-ion batteries (AZIBs) is becoming a research hotspot owing to its fast kinetics and additional capacities. However, H+ storage mechanism has not been deciphered in the popular MoS2 -based AZIBs. Herein, we innovatively prepared a MoS2 /poly(3,4-ethylenedioxythiophene) (MoS2 /PEDOT) hybrid, where the intercalated PEDOT not only increases the interlayer spacing (from 0.62 to 1.29 nm) and electronic conductivity of MoS2 , but also activates the proton insertion chemistry. Thus, highly efficient and reversible H+ /Zn2+ co-insertion/extraction behaviors are demonstrated for the first time in aqueous Zn-MoS2 batteries. More intriguingly, the co-inserted protons can act as lubricants to effectively shield the electrostatic interactions between MoS2 /PEDOT host and divalent Zn2+ , enabling the accelerated ion-diffusion kinetics and exceptional rate performance. This work proposes a new concept of "proton lubricant" driving Zn2+ transport and broadens the horizons of Zn-MoS2 batteries.

Using Machine Learning to Predict Oxygen Evolution Activity for Transition Metal Hydroxide Electrocatalysts.

Electrocatalytic water splitting is an attractive way to generate hydrogen and oxygen for obtaining clean energy. Oxygen evolution reaction (OER), as one of the half reactions of oxygen evolution, is kinetically unfavorable involving the transfer of four electrons. Hydroxides are promising candidates for efficient OER electrocatalysts toward water splitting because of their high intrinsic activity and active surface area. However, quantitative prediction of hydroxide electrocatalytic performances from high-dimensional component spaces remains a challenge, severely hindering the performance-oriented precise composition and process design. Herein, we introduce a machine learning-based OER activity prediction method for hydroxide catalysts under extensive doping space for the first time. The relationship among composition, morphology, phase, pH value of the electrolyte, type of the working electrode, and overpotential was successfully fitted by the random forest algorithm. The model shows a good precision on the forecast of new experiments with a mean relative error of 4.74%. Furthermore, a new high-activity hydroxide catalyst Ni0.77Fe0.13La0.1 was rationally designed and experimentally prepared, showing an ultra-low OP of 226 mV for a current density of 10 mA cm-2. This work provides an effective and novel way for hydroxide electrocatalyst prediction, which can further enhance the electrocatalyst design toward high catalytic performance.

Stabilized Multi-Electron Reactions in a High-Energy Na4 Mn0.9 CrMg0.1 (PO4 )3 Sodium-Storage Cathode Enabled by the Pinning Effect.

Na superionic conductor (NASICON)-type Na4 MnCr(PO4 )3 has attracted extensive attention among the phosphate sodium-storage cathodes due to its ultra-high energy density originating from three-electron reactions but it suffers from severe structural degradation upon repeated sodiation/desodiation processes. Herein, Mg is used for partial substitution of Mn in Na4 MnCr(PO4 )3 to alleviate Jahn-Teller distortions and to prolong the cathode cycling life by virtue of the pinning effect induced by implanting inert MgO6 octahedra into the NASICON framework. The as-prepared Na4 Mn0.9 CrMg0.1 (PO4 )3 /C cathode delivers high capacity retention of 92.7% after 500 cycles at 5 C and fascinating rate capability of 154.6 and 70.4 mAh g-1 at 0.1 and 15 C, respectively. Meanwhile, it can provide an admirable energy density of ≈558.48 Wh kg-1 based on ≈2.8-electron reactions of Mn2+ /Mn3+ , Mn3+ /Mn4+ , and Cr3+ /Cr4+ redox couples. In situ X-ray diffraction reveals the highly reversible single-phase and bi-phase structural evolution of such cathode materials with a volume change of only 6.3% during the whole electrochemical reaction. The galvanostatic intermittent titration technique and density functional theory computations jointly demonstrate the superior electrode process kinetics and enhanced electronic conductivity after Mg doping. This work offers a new route to improve the cycling stability of the high-energy NASICON-cathodes for sodium-ion batteries.

Recent Advances and Perspectives of Air Stable Sulfide-Based Solid Electrolytes for All-Solid-State Lithium Batteries.

An all-solid-state battery enabled by the incombustible and highly Li-ion conductive sulfide solid-state electrolyte, is recognized to be a strong candidate for next-generation of lithium-ion batteries. Intensive research efforts have been devoted to developing the well-suited sulfide electrolytes with outstanding performances. Although several types of sulfide electrolytes have achieved superionic conductivities with excellent deformability, the air-sensitive behaviors of them are detrimental to the large-scale production. Considerable efforts are in progress to tackle this issue via various strategies in recent years. This review provides an overview of several classes of promising sulfide solid electrolytes. The principle and strategies for improving the resistance of these sulfide electrolytes against air are thoroughly discussed. We also point out the major challenges that all-solid-state batteries and different types of sulfide electrolytes face for practical applications.

Design Concepts of Transition Metal Dichalcogenides for High-Performance Aqueous Zn-Ion Storage.

Aqueous Zn-ion batteries (AZIBs) are considered as promising large-scale energy storage devices due to their high safety and low cost. Transition metal dichalcogenides (TMDs) as the potential aqueous Zn-storage cathode materials are under the research spotlight because of their facile 2D ion-transport channels and weak electrostatic interactions with Zn2+ . In this concept article, we summarize the intrinsic structural features and aqueous Zn-storage mechanisms of the TMDs-based electrodes. More significantly, the latest design concepts of TMDs materials for high-performance AZIBs are discussed in detail from three aspects of interlayer expansion engineering, phase transition engineering, and structure defects engineering. Finally, the current challenges facing TMDs cathodes and possible remedies are outlined for future developments towards efficient, rapid, and stable aqueous Zn-ion storage.

Prediction of Oxygen Evolution Activity for NiCoFe Oxide Catalysts via Machine Learning.

Transition metal (such as Fe, Co, and Ni) oxides are excellent systems in the oxygen evolution reaction (OER) for the development of non-noble-metal-based catalysts. However, direct experimental evidence and the physical mechanism of a quantitative relationship between physical factors and oxygen evolution activity are still lacking, which makes it difficult to theoretically and accurately predict the oxygen evolution activity. In this work, a data-driven method for the prediction of overpotential (OP) for (Ni-Fe-Co)O x catalysts is proposed via machine learning. The physical features that are more related to the OP for the OER have been constructed and analyzed. The random forest regression model works exceedingly well on OP prediction with a mean relative error of 1.20%. The features based on first ionization energies (FIEs) and outermost d-orbital electron numbers (DEs) are the principal factors and their variances (δFIE and δDE) exhibit a linearly decreasing correlation with OP, which gives direct guidance for an OP-oriented component design. This method provides novel and promising insights for the prediction of oxygen evolution activity and physical factor analysis in (Ni-Fe-Co)O x catalysts.

Large-scale synthesis of ultrafine Fe3C nanoparticles embedded in mesoporous carbon nanosheets for high-rate lithium storage.

Fe3C modified by the incorporation of carbon materials offers excellent electrical conductivity and interfacial lithium storage, making it attractive as an anode material in lithium-ion batteries. In this work, we describe a time- and energy-saving approach for the large-scale preparation of Fe3C nanoparticles embedded in mesoporous carbon nanosheets (Fe3C-NPs@MCNSs) by solution combustion synthesis and subsequent carbothermal reduction. Fe3C nanoparticles with a diameter of ∼5 nm were highly crystallized and compactly dispersed in mesoporous carbon nanosheets with a pore-size distribution of 3-5 nm. Fe3C-NPs@MCNSs exhibited remarkable high-rate lithium storage performance with discharge specific capacities of 731, 647, 481, 402 and 363 mA h g-1 at current densities of 0.1, 1, 2, 5 and 10 A g-1, respectively, and when the current density reduced back to 0.1 A g-1 after 45 cycles, the discharge specific capacity could perfectly recover to 737 mA h g-1 without any loss. The unique structure could promote electron and Li-ion transfer, create highly accessible multi-channel reaction sites and buffer volume variation for enhanced cycling and good high-rate lithium storage performance.

Correction: Large-scale synthesis of ultrafine Fe3C nanoparticles embedded in mesoporous carbon nanosheets for high-rate lithium storage.

[This corrects the article DOI: 10.1039/D1RA08516F.].

Mesoporous Single Crystals with Fe-Rich Skin for Ultralow Overpotential in Oxygen Evolution Catalysis.

The oxygen evolution reaction (OER) is a key reaction in water splitting and metal-air batteries, and transition metal hydroxides have demonstrated the most electrocatalytic efficiency. Making the hydroxides thinner for more surface commonly fails to increase the active site number, because the real active sites are the edges. Up to now, the overpotentials of most state-of-the-art OER electrocatalysts at a current density of 10 mA cm-2 (η10 ) are still larger than 200 mV. Herein, a novel design of mesoporous single crystal (MSC) with an Fe-rich skin to boost the OER is shown. The edges around the mesopores provide lots of real active sites and the Fe modification on these sites further improves the intrinsic activity. As a result, an ultralow η10 of 185 mV is achieved, and the turnover frequency based on Fe atoms is as high as 16.9 s-1 at an overpotential of 350 mV. Moreover, the catalyst has an excellent catalytic stability, indicated by a negligible current drop after 10 000 cyclic voltammetry cycles. The catalyst enables Zn-air batteries to run stably over 270 h with a low charge voltage of 1.89 V. This work shows that MSC materials can provide new opportunities for the design of electrocatalysts.

Boosting Aqueous Zn/MnO2 Batteries via a Synergy of Edge/Defect-Rich Cathode and Dendrite-Free Anode.

Aqueous Zn/MnO2 batteries exhibit huge potential for grid-scale energy storage but suffer from poor cycling stability derived from both structural instability of cathode and Zn dendrite growth of anode. Here, we report a high-performance aqueous Zn/MnO2 battery with ZnSO4-based electrolyte, comprising a nanoparticle-like cathode with abundant surface oxygen defects (MO-Vo) and a dendrite-free Zn anode. The transformation from nanowire (α-MnO2) to nanoparticle (MO-Vo) was found by tuning the annealing conditions in an argon flow. Moreover, the small size of MO-Vo nanoparticles can effectively promote the spatially uniform distribution of volume stress during carrier intercalation, boosting the structural stability of the MO-Vo cathode. Moreover, it was found that the intercalation pseudocapacitive behavior of Zn2+ in the MO-Vo cathode can be strongly boosted by tailoring the surface oxygen defect of MnO2 based on the calculations and experiments, thereby achieving enhanced cycling stability and redox kinetics. Additionally, the addition of K2SO4 additive into the electrolyte can tailor the deposition behavior of Zn2+, enabling stable Zn stripping/plating without dendrites. Therefore, the assembled Zn/MO-Vo batteries exhibit a high energy density and excellent long-term cyclability over 1400 cycles. Besides, the reaction mechanism of pseudocapacitive Zn2+ intercalation and H+ intercalation for the MO-Vo cathode was revealed via ex situ characterizations.

Study on the Hot Deformation Characterization of Borated Stainless Steel by Hot Isostatic Pressing.

Borated stainless steel (BSS) specimens have a boron content of 1.86 wt%, and are prepared by hot isostatic pressing (HIP) conducted at different temperatures, ranging from 1000 to 1100 °C and a constant true strain rate (0.01, 0.1, 1 and 10 s-1). These tests, with observations and microstructural analysis, have achieved the hot deformation characteristics and mechanisms of BSS. In this research, the activation energy (Q) and Zener-Hollomon parameter (Z) were contrasted against the flow curves: Q = 442.35 kJ/mol. The critical conditions associated with the initiation of dynamic recrystallization (DRX) for BSS were precisely calculated based on the function between the strain hardening rate with the flow stress: at different temperatures from 1000 to 1100 °C: the critical stresses were 146.69-254.77 MPa and the critical strains were 0.022-0.044. The facts show that the boron-containing phase of BSS prevented the onset of DRX, despite the saturated boron in the austenite initiated DRX. The microstructural analysis showed that hot deformation promoted the generation of borides, which differed from the initial microstructure of HIP. The inhomogeneous distribution of elements in the boron-containing phase was caused by hot compression.