Ni Single-Atom Bual Catalytic Electrodes for Long Life and High Energy Efficiency Zinc-Iodine Batteries.

Zinc-iodine batteries (Zn-I2) are extremely attractive as the safe and cost-effective scalable energy storage system in the stationary applications. However, the inefficient redox kinetics and "shuttling effect" of iodine species result in unsatisfactory energy efficiency and short cycle life, hindering their commercialization. In this work, Ni single atoms highly dispersed on carbon fibers is designed and synthesized as iodine anchoring sites and dual catalysts for Zn-I2 batteries, and successfully inhibit the iodine species shuttling and boost dual reaction kinetics. Theoretical calculations indicate that the reinforced d-p orbital hybridization and charge interaction between Ni single-atoms and iodine species effectively enhance the confinement of iodine species. Ni single-atoms also accelerate the iodine conversion reactions with tailored bonding structure of I─I bonds and reduced energy barrier for the dual conversion of iodine species. Consequently, the high-rate performance (180 mAh g-1 at 3 A g-1), cycling stability (capacity retention of 74% after 5900 cycles) and high energy efficiency (90% at 3 A g-1) are achieved. The work provides an effective strategy for the development of iodine hosts with high catalytic activity for Zn-I2 batteries.

Tuning [VO6] Octahedron of Ammonium Vanadates via F Incorporation for High-Performance Aqueous Zinc Ion Batteries.

The electrochemical properties of vanadium-based materials as cathode materials for aqueous zinc ion batteries are still restricted by low conductivity, sluggish reaction kinetics, and poor structural stability. Herein, the [VO6] octahedron, as the basic unit of vanadium-oxide layer of ammonium vanadates (NH4V4O10, denoted as NVO), is incorporated by F atoms to regulate the coordinated environment of vanadium. Density functional theory (DFT) calculations and experimental results show that both physicochemical and electrochemical properties of NVO are improved by F-doping. The enhanced electronic conductivity accelerates the electron transfer and the expanded interlayer spacing expedites the diffusion kinetics of zinc ions. As a result, the F-doped NVO (F-NVO) electrode shows a high discharge capacity (465 mAh g-1 at 0.1 A g-1), good rate capability (260 mAh g-1 at 5 A g-1), and long-term cycling stability (88% capacity retention over 2000 cycles at 4 A g-1). The reaction kinetics and energy storage mechanism of F-NVO are further validated by in situ and ex situ characterizations.

NH4 + Pre-Intercalation and Mo Doping VS2 to Regulate Nanostructure and Electronic Properties for High Efficiency Sodium Storage.

Sodium-ion hybrid capacitors (SIHCs) have attracted much attention due to integrating the high energy density of battery and high out power of supercapacitors. However, rapid Na+ diffusion kinetics in cathode is counterbalanced with sluggish anode, hindering the further advancement and commercialization of SIHCs. Here, aiming at conversion-type metal sulfide anode, taking typical VS2 as an example, a comprehensive regulation of nanostructure and electronic properties through NH4 + pre-intercalation and Mo-doping VS2 (Mo-NVS2) is reported. It is demonstrated that NH4 + pre-intercalation can enlarge the interplanar spacing and Mo-doping can induce interlayer defects and sulfur vacancies that are favorable to construct new ion transport channels, thus resulting in significantly enhanced Na+ diffusion kinetics and pseudocapacitance. Density functional theory calculations further reveal that the introduction of NH4 + and Mo-doping enhances the electronic conductivity, lowers the diffusion energy barrier of Na+, and produces stronger d-p hybridization to promote conversion kinetics of Na+ intercalation intermediates. Consequently, Mo-NVS2 delivers a record-high reversible capacity of 453 mAh g-1 at 3 A g-1 and an ultra-stable cycle life of over 20 000 cycles. The assembled SIHCs achieve impressive energy density/power density of 98 Wh kg-1/11.84 kW kg-1, ultralong cycling life of over 15000 cycles, and very low self-discharge rate (0.84 mV h-1).

Using MXene as a Chemically Induced Initiator to Construct High-Performance Cathodes for Aqueous Zinc-Ion Batteries.

MXene usually exhibits weak pseudo-capacitance behavior in aqueous zinc-ion batteries, which cannot provide sufficient reversible capacity, resulting in the decline of overall capacity when used as the cathode materials. Taking inspiration from polymer electrolyte engineering, we have conceptualized an in-situ induced growth strategy based on MXene materials. Herein, 5.25 % MXene was introduced into the nucleation and growth process of vanadium oxide (HVO), providing the heterogeneous nucleation site and serving as an initiator to regulate the morphology and structural of vanadium oxide (T-HVO). The resulted materials can significantly improve the capacity and rate performance of zinc-ion batteries. The growth mechanism of T-HVO was demonstrated by both characterizations and DFT simulations, and the improved performance was systematically investigated through a series of in-situ experiments related to dynamic analysis steps. Finally, the evaluation and comparison of various defect introduction strategies revealed the efficient, safety, and high production output characteristics of the in-situ induced growth strategy. This work proposes the concept of in-situ induced growth strategy and discloses the induced chemical mechanism of MXene materials, which will aid the understanding, development, and application of cathode in aqueous zinc-ion batteries.

Sodium-Ion Substituted Water Molecule in Layered Vanadyl Phosphate Enhancing Electrochemical Kinetics and Stability of Zinc Ion Storage.

Vanadyl phosphate (VOPO4 ·2H2 O) has been regarded as one of the most promising cathode materials for aqueous Zn-ion batteries due to its distinct layered structure. However, VOPO4 ·2H2 O has not yet demonstrated the exceptional Zn ion storage performance owing to the structural deterioration during repeated charging/discharging process and poor intrinsic conductivity. In this work, 2D sodium vanadyl phosphate (NaVOPO4 ·0.83H2 O, denoted as NaVOP) is designed as a cathode material for Zn-ion batteries, in which sodium ions are preinserted into the interlayer, replacing part of water. Benefiting from the in situ surface oxidization, improved electronic conductivity, and increased hydrophobicity, the NaVOP electrode exhibits a high discharge capacity of 187 mAh g-1 at 0.1 A g-1 after activation, excellent rate capability and enhanced cycling performance with 85% capacity retention after 1500 cycles at 1 A g-1 . The energy storage mechanism of the NaVOP nanoflakes based on the rapid Zn2+ and H+ intercalation pseudocapacitance are investigated via multiple ex situ characterizations.

Enhanced Li+ Diffusion and Lattice oxygen Stability by the High Entropy Effect in Disordered-Rocksalt Cathodes.

Cation-disordered Rocksalt oxides (DRXs) are a promising new class of cathode materials for Li-ion batteries due to their natural abundance, low cost and great electrochemical performance. High entropy strategy in Mn-based DRXs appears to be an effective strategy for improving the rate capability, but it suffers from challenges including capacity degradation. The present paper reports a new group of high entropy DRXs (HE DRX) based on Ni2+ -Nb5+ pair; the structural and chemical evolution upon cycling of DRXs with an increasing transition metal (TM) species are systematically investigated. An explanation is proposed for how the crystal field stability energy determines that HE DRX could exist in single Rocksalt solid solution structures. We further reveal that the charge compensation mechanism in HE DRX is the result of various TM synergistic effect. More importantly, through various in situ and ex situ techniques and theoretical calculation, the effective integration of more TM cation species within the HE DRX framework promotes better Li+ diffusion and improves lattice oxygen stability, consequently increasing capacity upon cycling.

Layered Cathode Materials: Precursors, Synthesis, Microstructure, Electrochemical Properties, and Battery Performance.

The exploitation of clean energy promotes the exploration of next-generation lithium-ion batteries (LIBs) with high energy-density, long life, high safety, and low cost. Ni-rich layered cathode materials are one of the most promising candidates for next-generation LIBs. Numerous studies focusing on the synthesis and modifications of the layered cathode materials are published every year. Many physical features of precursors, such as density, morphology, size distribution, and microstructure of primary particles pass to the resulting cathode materials, thus significantly affecting their electrochemical properties and battery performance. This review focuses on the recent advances in the controlled synthesis of hydroxide precursors and the growth of particles. The essential parameters in controlled coprecipitation are discussed in detail. Some innovative technologies for precursor modifications and for the synthesis of novel precursors are highlighted. In addition, future perspectives of the development of hydroxide precursors are presented.

Active Materials for Aqueous Zinc Ion Batteries: Synthesis, Crystal Structure, Morphology, and Electrochemistry.

Aqueous zinc ion batteries (ZIBs) are truly promising contenders for the future large-scale electrical energy storage applications due to their cost-effectiveness, environmental friendliness, intrinsic safety, and competitive gravimetric energy density. In light of this, massive research efforts have been devoted to the design and development of high-performance aqueous ZIBs; however, there are still obstacles to overcome before realizing their full potentials. Here, the current advances, existing limitations, along with the possible solutions in the pursuit of cathode materials with high voltage, fast kinetics, and long cycling stability are comprehensively covered and evaluated, together with an analysis of their structures, electrochemical performance, and zinc ion storage mechanisms. Key issues and research directions related to the design of highly reversible zinc anodes, the exploration of electrolytes satisfying both low cost and good performance, as well as the selection of compatible current collectors are also discussed, to guide the future design of aqueous ZIBs with a combination of high gravimetric energy density, good reversibility, and a long cycle life.

Tailoring Pore Structures of 3D Printed Cellular High-Loading Cathodes for Advanced Rechargeable Zinc-Ion Batteries.

Developing high-loading cathodes with superior electrochemical performance is desirable but challenging in aqueous zinc-ion batteries (ZIBs) for commercialization. Advanced 3D printing of cellular and hierarchical porous cathodes with high mass loading for superior ZIBs is explored here. To obtain a high-performance 3D printable ink, a composite material of iron vanadate and reduced holey graphene oxide is synthesized as the ink component. A cellular cathode with hierarchical porous architecture for aqueous ZIBs is then designed and fabricated by 3D printing for the first time. The unique structures of 3D printed composite cathode provide interpenetrating transmission paths as well as channels for electrons and ions. 3D printed cathodes with high mass loading over 10 mg cm-2 exhibit a high specific capacity of 344.8 mAh g-1 at 0.1 A g-1 and deliver outstanding cycling stability over 650 cycles at 2 A g-1 . In addition, the printing strategy enables the ease increase in mass loading up to 24.4 mg cm-2 , where a remarkably high areal capacity of 7.04 mAh cm-2 is reached. The superior electrochemical performance paves the new way to design the state-of-the-art cathodes for ZIBs.

In Situ Defect Induction in Close-Packed Lattice Plane for the Efficient Zinc Ion Storage.

In situ electrochemical activation brings unexpected electrochemical performance improvements to electrode materials, but the mechanism behind it still needs further study. Herein, an electrochemically in situ defect induction in close-packed lattice plane of vanadium nitride oxide (VNx Oy ) in aqueous zinc-ion battery is reported. It is verified by theoretical calculation and experiment that the original compact structure is not suitable for the insert of Zn2+ ion, while a highly active one after the initial electrochemical activization accompanied by the in situ defect induction in close-packed lattice plane of VNx Oy exhibits efficient zinc ion storage. As expected, activated VNx Oy can achieve very high reversible capacity of 231.4 mA h g-1 at 1 A g-1 and cycle stability upto 6000 cycles at 10 A g-1 with a capacity retention of 94.3%. This work proposes a new insight for understanding the electrochemically in situ transformation to obtain highly active cathode materials for the aqueous zinc-ion batteries.

Direct Ink Writing of Li1.3 Al0.3 Ti1.7 (PO4 )3 -Based Solid-State Electrolytes with Customized Shapes and Remarkable Electrochemical Behaviors.

All-solid-state lithium batteries have received extensive attention due to their high safety and promising energy density and are considered as the next-generation electrochemical energy storage system. However, exploring solid-state electrolytes in customized geometries without sacrificing the ionic transport is significant yet challenging. Herein, various 3D printable Li1.3 Al0.3 Ti1.7 (PO4 )3 (LATP)-based inks are developed to construct ceramic and hybrid solid-state electrolytes with arbitrary shapes as well as high conductivities. The obtained inks show suitable rheological behaviors and can be successfully extruded into solid-state electrolytes using the direct ink writing (DIW) method. As-printed free-standing LATP ceramic solid-state electrolytes deliver high ionic conductivity up to 4.24 × 10-4  S cm-1 and different shapes such as "L", "T," and "+" can be easily realized without sacrificing high ionic transport properties. Moreover, using this printing method, LATP-based hybrid solid-state electrolytes can be directly printed on LiFePO4 cathodes for solid-state lithium batteries, where a high discharge capacity of 150 mAh g-1 at 0.5 C is obtained. The DIW strategy for solid-state electrolytes demonstrates a new way toward advanced solid-state energy storage with the high ionic transport and customized manufacturing ability.

The NHx Group Induced Formation of 3D α-Co(OH)2 Curly Nanosheet Aggregates as Efficient Oxygen Evolution Electrocatalysts.

Recently, the curly structure attracts researchers' attention due to the strain effect, electronic effect, and improved surface area, which exhibits enhanced electrocatalytic activity. However, the synthesis of metastable curved structures is very difficult. Herein, a simple room temperature coprecipitation method is proposed to synthesize 3D cobalt (Co) hydroxide (α-Co(OH)2 ) electrocatalysts that consist of curly 2D nanosheets. The formation process of curly nanosheets is elaborated systematically and the results demonstrate that the NHx group has great effect on the formation of curly structure. Combining the advantage of 2D curly nanosheet and 3D aggregate structure, the as-prepared α-Co(OH)2 curly nanosheet aggregates show the best water oxidation activity with an overpotential of 269 mV at j = 10 mA cm-2 in 1.0 m KOH. The electrocatalytic process studies demonstrate that the formation of CoIV O species is the rate-determining step. Theoretical calculations further confirm the beneficial effect of the bent structure on the conductivity, the adsorption of OH- and the formation of OOH* species.

Engineering Halide Perovskite Crystals through Precursor Chemistry.

The composition, crystallinity, morphology, and trap-state density of halide perovskite thin films critically depend on the nature of the precursor solution. A fundamental understanding of the liquid-to-solid transformation mechanism is thus essential to the fabrication of high-quality thin films of halide perovskite crystals for applications such as high-performance photovoltaics and is the topic of this Review. The roles of additives on the evolution of coordination complex species in the precursor solutions and the resulting effect on perovskite crystallization are presented. The influence of colloid characteristics, DMF/DMSO-free solutions and the degradation of precursor solutions on the formation of perovskite crystals are also discussed. Finally, the general formation mechanism of perovskite thin films from precursor solutions is summarized and some questions for further research are provided.

Graphene-Encapsulated FeS2 in Carbon Fibers as High Reversible Anodes for Na+ /K+ Batteries in a Wide Temperature Range.

Developing low cost, long life, and high capacity rechargeable batteries is a critical factor towards developing next-generation energy storage devices for practical applications. Therefore, a simple method to prepare graphene-coated FeS2 embedded in carbon nanofibers is employed; the double protection from graphene coating and carbon fibers ensures high reversibility of FeS2 during sodiation/desodiation and improved conductivity, resulting in high rate capacity and long-term life for Na+ (305.5 mAh g-1 at 3 A g-1 after 2450 cycles) and K+ (120 mAh g-1 at 1 A g-1 after 680 cycles) storage at room temperature. Benefitting from the enhanced conductivity and protection on graphene-encapsulated FeS2 nanoparticles, the composites exhibit excellent electrochemical performance under low temperature (0 and -20 °C), and temperature tolerance with stable capacity as sodium-ion half-cells. The Na-ion full-cells based on the above composites and Na3 V2 (PO4 )3 can afford reversible capacity of 95 mAh g-1 at room temperature. Furthermore, the full-cells deliver promising discharge capacity (50 mAh g-1 at 0 °C, 43 mAh g-1 at -20 °C) and high energy density at low temperatures. Density functional theory calculations imply that graphene coating can effectively decrease the Na+ diffusion barrier between FeS2 and graphene heterointerface and promote the reversibility of Na+ storage in FeS2 , resulting in advanced Na+ storage properties.

High Energy Capacitors Based on All Metal-Organic Frameworks Derivatives and Solar-Charging Station Application.

High energy and efficient solar charging stations using electrochemical capacitors (ECs) are a promising portable power source for the future. In this work, two kinds of metal-organic framework (MOF) derivatives, NiO/Co3 O4 microcubes and Fe2 O3 microleaves, are prepared via thermal treatment and assembled into electrochemical capacitors, which deliver a relatively high specific energy density of 46 Wh kg-1 at 690 W kg-1 . In addition, a solar-charging power system consisting of the electrochemical capacitors and monocrystalline silicon plates is fabricated and a motor fan or 25 LEDs for 5 and 30 min, respectively, is powered. This work not only adds two novel materials to the growing categories of MOF-derived advanced materials, but also successfully achieves an efficient solar-ECs system for the first time based on all MOF derivatives, which has a certain reference for developing efficient solar-charge systems.

Interface Engineering V2 O5 Nanofibers for High-Energy and Durable Supercapacitors.

A local electric field is induced to engineer the interface of vanadium pentoxide nanofibers (V2 O5 -NF) to manipulate the charge transport behavior and obtain high-energy and durable supercapacitors. The interface of V2 O5 -NF is modified with oxygen vacancies (Vö) in a one-step polymerization process of polyaniline (PANI). In the charge storage process, the local electric field deriving from the lopsided charge distribution around Vö will provide Coulombic forces to promote the charge transport in the resultant Vö-V2 O5 /PANI nanocable electrode. Furthermore, an ≈7 nm porous PANI coating serves as the external percolated charge transport pathway. As the charge transfer kinetics are synergistically enhanced by the dual modifications, Vö-V2 O5 /PANI-based supercapacitors exhibit an excellent specific capacitance (523 F g-1 ) as well as a long cycling lifespan (110% of capacitance remained after 20 000 cycles). This work paves an effective way to promote the charge transfer kinetics of electrode materials for next-generation energy storage systems.

Low Temperature Synthesis of Large-Size Anatase TiO2 Nanosheets with Enhanced Photocatalytic Activities.

TiO2 nanosheets have continuously been intriguing due to their high surface activities as photocatalyst but still challenging to synthesis large-scale 2D nanostructures. A special microstructure evolution of TiO2 , ripening in aqueous solution at low temperature (≈4 °C), is found for the first time, i.e., from the initial aperiodic atom-networks gradually into low crystallized continuous spongy structure with small crystal facets and ultimately forming large-size anatase nanosheets with exposed (101) and (200) facets. Based on this finding, the synthesized anatase TiO2 nanosheets possess monodispersed large-scale 2D nanostructure so as to exhibit appreciable quantum size effects and remarkable enhanced optical absorption capacity. Using photocatalytic reduction of Cr (VI) to Cr (III) as the probe reaction to evaluate photocatalytic activities of the TiO2 nanosheets, the reductivity of Cr (VI) achieves 99.8% in 15 min under irradiation of 200-800 nm light. At the same time, an in situ Cr (III)-doping occurs spontaneously and triggers pronounced visible light driven photocatalysis, reducing 99% of Cr (VI) in 100 min under irradiation of 400-800 nm light.

A Phase-Separation Route to Synthesize Porous CNTs with Excellent Stability for Na+ Storage.

Porous carbon nanotubes (CNTs) are obtained by removing MoO2 nanoparticles from MoO2 @C core@shell nanofibers which are synthesized by phase-segregation via a single-needle electrospinning method. The specific surface area of porous CNTs is 502.9 m2 g-1 , and many oxygen-containing functional groups (COH, CO) are present. As anodes for sodium-ion batteries, the porous CNT electrode displays excellent rate performance and cycling stability (110 mA h g-1 after 1200 cycles at 5 A g-1 ). Those high properties can be attributed to the porous structure and surface modification to steadily store Na+ with high capacity. The work provides a facile and broadly applicable way to fabricate the porous CNTs and their composites for batteries, catalysts, and fuel cells.

Enhanced Electrochemical Properties of Li3 VO4 with Controlled Oxygen Vacancies as Li-Ion Battery Anode.

Li3 VO4 , as a promising intercalation-type anode material for lithium-ion batteries, features a desired discharge potential (ca. 0.5-1.0 V vs. Li/Li+ ) and a good theoretical storage capacity (590 mAh g-1 with three Li+ inserted). However, the poor electrical conductivity of Li3 VO4 hinders its practical application. In the present work, various amounts of oxygen vacancies were introduced in Li3 VO4 through annealing in hydrogen to improve its conductivity. To elucidate the influence of oxygen vacancies on the electrochemical performances of Li3 VO4 , the surface energy of the resulting material was measured with an inverse gas chromatography method. It was found that Li3 VO4 annealed in pure hydrogen at 400 °C for 15 min exhibited a much higher surface energy (60.7 mJ m-2 ) than pristine Li3 VO4 (50.6 mJ m-2 ). The increased surface energy would lower the activation energy of phase transformation during the charge-discharge process, leading to improved electrochemical properties. As a result, the oxygen-deficient Li3 VO4 achieved a significantly improved specific capacity of 495 mAh g-1 at 0.1 Ag-1 (381 mAh g-1 for pristine Li3 VO4 ) and retains 165 mAh g-1 when the current density increases to 8 Ag-1 .

One-pot synthesis of in-situ carbon-coated Fe3O4 as a long-life lithium-ion battery anode.

Fe3O4 has been regarded as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity, low cost, and environmental friendliness. In this work, we present a one-pot reducing-composite-hydroxide-mediated (R-CHM) method to synthesize in situ carbon-coated Fe3O4 (Fe3O4@C) at 280 °C using Fe(NO3)3 · 9H2O and PEG800 as raw materials and NaOH/KOH as the medium. The as-prepared Fe3O4 octahedron has an average size of 100 nm in diameter, covered by a carbon layer with a thickness of 3 nm, as revealed by FESEM and HRTEM images. When used as anode materials in LIBs, Fe3O4@C exhibited an outstanding rate capability (1006, 918, 825, 737, 622, 455 and 317 mAh g-1 at 0.1, 0.2, 0.5, 0.8, 1.0, 1.5 and 2.0 A g-1). Moreover, it presented an excellent cycling stability, with a retained capacity of 261 mAh g-1 after 800 cycles under an extremely high specific current density of 2.0 A g-1. Such results indicate that Fe3O4@C can provide a new route into the development of long-life electrodes for future rechargeable LIBs. Importantly, the R-CHM developed in our work can be extended for the synthesis of other carbon-coated electrodes for LIBs and functional nanostructures for broader applications.