Ion adsorption promotes Frank-van der Merwe growth of 2D transition metal tellurides.

Reliable synthesis methods for high-quality, large-sized, and uniform two-dimensional (2D) transition-metal dichalcogenides (TMDs) are crucial for their device applications. However, versatile approaches to growing high-quality, large-sized, and uniform 2D transition-metal tellurides are rare. Here, we demonstrate an ion adsorption strategy that facilitates the Frank-van der Merwe growth of 2D transition-metal tellurides. By employing this method, we grow MoTe2 and WTe2 with enhanced lateral size, reduced thickness, and improved uniformity. Comprehensive characterizations confirm the high quality of as-grown MoTe2. Moreover, various characterizations verify the adsorption of K+ and Cl- ions on the top surface of MoTe2. X-ray photoelectron spectroscopy (XPS) analysis reveals that the MoTe2 is stoichiometric without K+ and Cl- ions and exhibits no discernable oxidation after washing. This top surface control strategy provides a new controlling knob to optimize the growth of 2D transition-metal tellurides and holds the potential for generalized to other 2D materials.

Low-strain and ultra-long cycle stability large-diameter soft carbon microsphere potassium ion anode.

Potassium-ion batteries (PIBs) with high potassium abundance, low redox potential of K/K+ and similar energy storage mechanism to lithium-ion batteries are potential candidates for large-scale energy storage in the future. However, due to the large size of K+ (1.38 Å), PIBs exhibit poor kinetics in existing commercial graphite anode materials system. Additionally, they can degrade the material structure and induce significant volume effects, leading to material fragmentation and pulverization in the process of long cycling. It is not straightforward to achieve compatibility with existing potassium anode systems, which forces us to develop new high-performance, low-strain anode materials with outstanding structural stability. Hence, nitrogen doping low-strain and large diameter soft carbon microspheres (NDCS) anodes were successfully developed to meet the demands of high-performance PIBs. Due to its large diameter and low strain characteristics, the Coulomb efficiency is as high as 98.7 %, and the capacity retention is close to 70 % after 4000 cycles at a current density of 1 A/g. Furthermore, we employed advanced computed tomography (CT) techniques to enhance the comprehension of electrochemically driven reactions from the surface to the bulk. This work provides a promising and viable technical solution for exploring PIBs anode materials with low strain and long cycling capabilities to meet the requirements of various application scenarios.

New Emerging Fast Charging Microscale Electrode Materials.

Fast charging lithium (Li)-ion batteries are intensively pursued for next-generation energy storage devices, whose electrochemical performance is largely determined by their constituent electrode materials. While nanosizing of electrode materials enhances high-rate capability in academic research, it presents practical limitations like volumetric packing density and high synthetic cost. As an alternative to nanosizing, microscale electrode materials cannot only effectively overcome the limitations of the nanosizing strategy but also satisfy the requirement of fast-charging batteries. Therefore, this review summarizes the new emerging microscale electrode materials for fast charging from the commercialization perspective. First, the fundamental theory of electronic/ionic motion in both individual active particles and the whole electrode is proposed. Then, based on these theories, the corresponding optimization strategies are summarized toward fast-charging microscale electrode materials. In addition, advanced functional design to tackle the mechanical degradation problems related to next generation high capacity alloy- and conversion-type electrode materials (Li, S, Si et al.) for achieving fast charging and stable cycling batteries. Finally, general conclusions and the future perspective on the potential research directions of microscale electrode materials are proposed. It is anticipated that this review will provide the basic guidelines for both fundamental research and practical applications of fast-charging batteries.

Insights into Electrode Architectures and Lithium-Ion Transport in Polycrystalline V2 O5 Cathodes of Solid-State Batteries.

Polymer-based solid-state batteries (SSBs) have received increasing attentions due to the absence of interfacial problems in sulfide/oxide-type SSBs, but the lower oxidation potential of polymer-based electrolytes greatly limits the application of conventional high-voltage cathode such as LiNix Coy Mnz O2 (NCM) and lithium-rich NCM. Herein, this study reports on a lithium-free V2 O5 cathode that enables the applications of polymer-based solid-state electrolyte (SSE) with high energy density due to the microstructured transport channels and suitable operational voltage. Using a synergistic combination of structural inspection and non-destructive X-ray computed tomography (X-CT), it interprets the chemo-mechanical behavior that determines the electrochemical performance of the V2 O5 cathode. Through detailed kinetic analyses such as differential capacity and galvanostatic intermittent titration technique (GITT), it is elucidated that the hierarchical V2 O5 constructed through microstructural engineering exhibits smaller electrochemical polarization and faster Li-ion diffusion rates in polymer-based SSBs than those in the liquid lithium batteries (LLBs). By the hierarchical ion transport channels created by the nanoparticles against each other, superior cycling stability (≈91.7% capacity retention after 100 cycles at 1 C) is achieved at 60 °C in polyoxyethylene (PEO)-based SSBs. The results highlight the crucial role of microstructure engineering in designing Li-free cathodes for polymer-based SSBs.

Self-Healing of Prussian Blue Analogues with Electrochemically Driven Morphological Rejuvenation.

Maintaining the morphology of electrode materials with high invertibility contributes to the prolonged cyclic stability of battery systems. However, the majority of electrode materials tend to degrade during the charge-discharge process owing to the inevitable increase in entropy. Herein, a self-healing strategy is designed to promote morphology rejuvenation in Prussian blue analogue (PBA) cathodes by cobalt doping. Experimental characterization and theoretical calculations demonstrate that a trace amount of cobalt can decelerate the crystallization process and restore the cracked areas to ensure perfect cubic structures of PBA cathodes. The electric field controls the kinetic dynamics, rather than the conventional thermodynamics, to realize the "electrochemically driven dissolution-recrystallization process" for the periodic self-healing phenomenon. The properties of electron transportation and ion diffusion in bulk PBA are also improved by the doping strategy, thus boosting the cyclability with 4000 cycles in a diluent electrolyte. This discovery provides a new paradigm for the construction of self-healing electrodes for cathodes.

Controllable and Homogeneous Lithium Electrodeposition via Lithiophilic Anchor Points.

Uncontrollable growth of lithium (Li) dendrites and low Coulombic efficiency induce security hazards and a short cycling lifespan of Li metal batteries. In this study, well-aligned ZnO nanorods on a periodic three-dimensional (3D) copper mesh (CM) are modified as lithiophilic anchor points to regulate the electrodeposition behavior of Li metal anodes. The in situ generated LiZn/Li2O arrays can efficiently guide the homogeneous Li electrodeposition along the nanorods. The porous structure of CM provides void space for the well-controlled lateral growth of Li starting from nanorod arrays. Moreover, the high surface area generated by both CM and the ZnO nanorods favors the charge transfer with low local current densities along the anode. Compared with bare Li anodes, Li-ZnO@CM anodes exhibited prolonged cycling stability for symmetric cells and superior capacity retention within Li/LiFePO4 full cells, demonstrating the effective design principles of ZnO@CM for stabilizing Li metal batteries.

Controlled Synthesis of a Two-Dimensional Non-van der Waals Ferromagnet toward a Magnetic Moiré Superlattice.

Two-dimensional (2D) magnetic materials provide an ideal platform for spintronics, magnetoelectrics, and numerous intriguing physical phenomena in 2D limits. Moiré superlattices based on 2D magnets offer an avenue for controlling the spin degree of freedom and engineering magnetic properties. However, the synthesis of high-quality, large-grain, and stable 2D magnets, much less obtaining a magnetic moiré superlattice, is still challenging. We synthesize 2D ferromagnets (trigonal Cr5Te8) with controlled thickness and robust stability through chemical vapor deposition. Single-unit-cell-thick flakes with lateral sizes of tens of micrometers are obtained. We observe the layer-by-layer growth mode for the crystal formation in non-van der Waals Cr5Te8. The robust anomalous Hall signal confirms that Cr5Te8 of varying thickness have a long-range ferromagnetic order with an out-of-plane easy axis. There is no obvious change of the Curie temperature when the thickness of Cr5Te8 decreases from 52.1 to 7.2 nm. Here, we construct diverse 2D non-van der Waals/van der Waals vertical heterostructures (Cr5Te8/graphene, Cr5Te8/h-BN, Cr5Te8/MoS2). A uniform moiré superlattice is formed in the heterostructure through a lattice mismatch. The successful growth of 2D Cr5Te8 and a related moiré superlattice introduces 2D non-van der Waals ferromagnets into moiré superlattice research, thus highlighting prospects for property investigation of a non-van der Waals magnetic moiré superlattice and massive applications which require a scalable approach to magnetic moiré superlattices.

Scalable and Versatile Transfer of Sensitive Two-dimensional Materials.

Damage-free transfer of large-area two-dimensional (2D) materials is indispensable to unleash their full potentials in a wide range of electronic, photonic, and biochemical applications. However, the all-surface nature of 2D materials renders many of them vulnerable to surrounding environments, especially etchants and water involved during wet transfer process. Up to now, a scalable and damage-free transfer method for sensitive 2D materials is still lacking. Here, we report a general damage-free transfer method for sensitive 2D materials. The as-transferred 2D materials exhibit well-preserved structural integrity and unaltered physical properties. We further develop a facile TEM sample preparation technique that allows direct recycling of materials on TEM grids with high fidelity. This recycling technique provides an unprecedented opportunity to precisely relate structural characterization with physical/chemical/electrical probing for the same samples. This method can be readily generalized to diverse nanomaterials for large-area damage-free transfer and enables in-depth investigation of structure-property relationship.

Hierarchical Stratiform of a Fluorine-Doped NiO Prism as an Enhanced Anode for Lithium-Ion Storage.

Doping is regarded as a prominent strategy to optimize the crystal structure and composition of battery materials to withstand the anisotropic expansion induced by the repeated insertion and extraction of guest ions. The well-known knowledge and experience obtained from doping engineering predominate in cathode materials but have not been fully explored for anodes yet. Here, we propose the practical doping of fluorine ions into the host lattice of nickel oxide to unveil the correlation between the crystal structure and electrochemical properties. Multiple ion transmission pathways are created by the orderly two-dimensional nanosheets, and thus the stress/strain can be significantly relieved with trace fluorine doping, ensuring the mechanical integrity of the active particle and superior electrochemical properties. Density functional theory calculations manifest that the F doping in NiO could improve crystal structural stability, modulate the charge distribution, and enhance the conductivity, which promotes the performance of lithium-ion storage.

Nitrogen and Fluorine Dual Doping of Soft Carbon Nanofibers as Advanced Anode for Potassium Ion Batteries.

Potassium-ion batteries (PIBs) are recognized as promising alternatives for lithium-ion batteries as the next-generation energy storage systems. However, the larger radius of K+ hinders the K+ insertion into the conventional carbon electrode and results in sluggish potassiation kinetics and poor cycling stability. Here, nitrogen and fluorine dual doping of soft carbon nanotubes (NFSC) anode are synthesized in one pot, achieving extraordinary electrochemical performance for PIBs. It is demonstrated that NFSC with a doping dose of 5.6 at% nitrogen and 1.3 at% fluorine together exhibits the highest reversible capacity of 238 mAh g-1 at 0.2 A g-1 and cycling stability of 186 mAh g-1 after 1000 cycles at 1 A g-1 . The extraordinary electrochemical performance can be attributed to the hollow structure, expanded interlayer distance, nitrogen and fluorine dual doping, and the binding ability of abundant defect sites. Moreover, density functional theory shows that the extra fluorine modification can dramatically enhance the conventional nitrogen doping effect and reduces the formation energy which makes a great contribution to the improvement of electrical conduction and K-ions insert. This work may promote the development of low-cost and sustainable carbon-based materials for PIBs and other advanced energy storage devices.

Fe-modified Co2(OH)3Cl microspheres for highly efficient oxygen evolution reaction.

Surface self-reconstruction by the electrochemical activation is considered as an effective strategy to increase the oxygen evolution reaction (OER) performance of transition metal compounds. Herein, uniform Co2(OH)3Cl microspheres are developed and present an activation-enhanced OER performance caused by the etching of lattice Cl- after 500 cyclic voltammetry (CV) cycles. Furthermore, the OER activity of Co2(OH)3Cl can be further enhanced after small amounts of Fe modification (Fe2+ as precursor). Fe doping into Co2(OH)3Cl lattices can make the etching of surface lattice Cl- easier and generate more surface vacancies to absorb oxygen species. Meanwhile, small amounts of Fe modification can result in a moderate surface oxygen adsorption affinity, facilitating the activation of intermediate oxygen species. Consequently, the 10% Fe-Co2(OH)3Cl exhibits a superior OER activity with a lower overpotential of 273 mV at 10 mA cm-2 (after 500 CV cycles) along with an excellent stability as compared with commercial RuO2.

Controllable synthesis of hierarchical MoS2 nanotubes with ultra-uniform and superior storage potassium properties.

Molybdenum disulfide (MoS2) is a promising nanomaterial which has been extensively investigated in photo-/electro-catalysis, sensors, and batteries due to its excellent physical/chemical properties. In this manuscript, MoS2 hierarchical nanotubes with hollow nanostructure are successfully synthesized via a facile hydrothermal method. SEM indicates that such MoS2 nanotubes have perfect uniformity while TEM demonstrates the hollow structure. Specifically, the ratio of MoS2 to the randomly produced polysulfide in the synthesized MoS2 nanotubes is 4.29 which confirms that the synthesized MoS2 nanotubes have quite high quality. Compared with the previous studies, our MoS2 nanotubes show superior rate capability and cyclability (127 mAh g-1 at 200 mA g-1 after 100 cycles) in the potassium ion battery.

Flexible Electrospun Carbon Nanofiber/Tin(IV) Sulfide Core/Sheath Membranes for Photocatalytically Treating Chromium(VI)-Containing Wastewater.

We report an efficient method for fabricating flexible membranes of electrospun carbon nanofiber/tin(IV) sulfide (CNF@SnS2) core/sheath fibers. CNF@SnS2 is a new photocatalytic material that can be used to treat wastewater containing high concentrations of hexavalent chromium (Cr(VI)). The hierarchical CNF@SnS2 core/sheath membranes have a three-dimensional macroporous architecture. This provides continuous channels for the rapid diffusion of photoelectrons generated by SnS2 nanoparticles under visible light irradiation. The visible light (λ > 400 nm) driven photocatalytic properties of CNF@SnS2 are evaluated by the reduction of water-soluble Cr(VI). CNF@SnS2 exhibits high visible light-driven photocatalytic activity because of its low band gap of 2.34 eV. Moreover, CNF@SnS2 exhibits good photocatalytic stability and excellent cycling stability. Under visible light irradiation, the optimized CNF@SnS2 membranes exhibit a high rate of degradation of 250 mg/L of aqueous Cr(VI) and can completely degrade the Cr(VI) within 90 min.

Fabrication of Unique Magnetic Bionanocomposite for Highly Efficient Removal of Hexavalent Chromium from Water.

Biotreatment of hexavalent chromium has attracted widespread interest due to its cost effective and environmental friendliness. However, the difficult separation of biomass from aqueous solution and the slow hexavalent chromium bioreduction rate are bottlenecks for biotechnology application. In this approach, a core-shell structured functional polymer coated magnetic nanocomposite was prepared for enriching the hexavalent chromium. Then the nanocomposite was connected to the bacteria via amines on bacterial (Bacillus subtilis ATCC-6633) surface. Under optimal conditions, a series of experiments were launched to degrade hexavalent chromium from the aqueous solution using the as-prepared bionanocomposite. Results showed that B. subtilis@Fe3O4@mSiO2@MANHE (BFSM) can degrade hexavalent chromium from the water more effectively (a respectable degradation efficiency of about 94%) when compared with pristine B. subtilis and Fe3O4@mSiO2@MANHE (FSM). Moreover, the BFSM could be separated from the wastewater by magnetic separation technology conveniently due to the Fe3O4 core of FSM. These results indicate that the application of BFSM is a promising strategy for effective treating wastewater containing hexavalent chromium.