Construction of VS2/VOx Heterostructure via Hydrolysis-Oxidation Coupling Reaction with Superior Sodium Storage Properties

Heterostructure engineering is one of the most promising modification strategies for reinforcing Na⁺ storage of transition metal sulfides. Herein, based on the spontaneous hydrolysis-oxidation coupling reaction of transition metal sulfides in aqueous media, a VO_x layer is induced and formed on the surface of VS₂, realizing tight combination of VS₂ and VO_x at the nanoscale and constructing homologous VS₂/VO_x heterostructure. Benefiting from the built-in electric field at the heterointerfaces, high chemical stability of VO_x, and high electrical conductivity of VS₂, the obtained VS₂/VO_x electrode exhibits superior cycling stability and rate properties. In particular, the VS₂/VO_x anode shows a high capacity of 878.2 mAh g⁻¹ after 200 cycles at 0.2 A g⁻¹. It also exhibits long cycling life (721.6 mAh g⁻¹ capacity retained after 1000 cycles at 2 A g⁻¹) and ultrahigh rate property (up to 654.8 mAh g⁻¹ at 10 A g⁻¹). Density functional theory calculations show that the formation of heterostructures reduces the activation energy for Na⁺ migration and increases the electrical conductivity of the material, which accelerates the ion/electron transfer and improves the reaction kinetics of the VS₂/VO_x electrode.     

Electrical Conductivity Adjustment for Interface Capacitive-Like Storage in Sodium-Ion Battery

Sodium-ion battery (SIB) is significant for grid-scale energy storage. However, a large radius of Na ions raises the difficulties of ion intercalation, hindering the electrochemical performance during fast charge/discharge. Conventional strategies to promote rate performance focus on the optimization of ion diffusion. Improving interface capacitive-like storage by tuning the electrical conductivity of electrodes is also expected to combine the features of the high energy density of batteries and the high power density of capacitors. Inspired by this concept, an oxide-metal sandwich 3D-ordered macroporous architecture (3DOM) stands out as a superior anode candidate for high-rate SIBs. Taking Ni-TiO₂ sandwich 3DOM as a proof-of-concept, anatase TiO₂ delivers a reversible capacity of 233.3 mAh g⁻¹ in half-cells and 210.1 mAh g⁻¹ in full-cells after 100 cycles at 50 mA g⁻¹. At the high charge/discharge rate of 5000 mA g⁻¹, 104.4 mAh g⁻¹ in half-cells and 68 mAh g⁻¹ in full-cells can also be obtained with satisfying stability. In-depth analysis of electrochemical kinetics evidence that the dominated interface capacitive-like storage enables ultrafast uptaking and releasing of Na-ions. This understanding between electrical conductivity and rate performance of SIBs is expected to guild future design to realize effective energy storage.     

Metal-Electronegativity-Induced,Synchronously Formed Hetero- and Vacancy-Structures of Selenide Molybdenum for Non-Aqueous Sodium-Based Dual-Ion Storage

Sodium-based dual-ion batteries (SDIBs) have attracted increasing research interests in energy storage systems because of their advantages of high operating voltage and low cost. However, exploring desirable anode materials with high capacity and stable structures remains a great challenge. Here, an elaborate design is reported, starting from well-organized MoSe₂ nanorods and introducing metal-organic frameworks, which simultaneously forms a bimetallic selenide/carbon composite with coaxial structure via electronegativity induction. By rationally adjusting the vacancy concentration and combining heterostructure engineering, the optimized MoSe_2-x/ZnSe@C as anode material for Na-ion batteries achieves rapid electrochemical kinetics and satisfactory reversible capacities. The systematic electrochemical kinetic analyses combined with theoretical calculations further unveil the synergistic effect of Se-vacancies and heterostructure for the enhanced sodium storage, which not only induces more reversible Na⁺ storage sites but also improves the pseudocapacitance and reduce charge transfer resistance, thereby providing a great contribution to accelerating reaction kinetics. Furthermore, the as-constructed SDIB full cell based on the MoSe_2-x/ZnSe@C anode and the expanded graphite cathode demonstrates impressively excellent rate performance (131 mAh g⁻¹ at 4.0 A g⁻¹) and ultralong cycling life over 1000 cycles (100 mAh g⁻¹ at 1.0 A g⁻¹), demonstrating its practical applicability in a wide range of sodium-based energy storage devices.     

Optimized Ti?O Subcompounds and Elastic Expanded MXene Interlayers Boost Quick Sodium Storage Performance

To develop quick-charge sodium-ion battery, it is significant to optimize insertion-type anode to afford fast Na⁺ diffusion rate and excellent electron conductivity. First-principles calculations reveal the Ti O subcompound superiority for Na⁺ diffusion following Ti(II) O > Ti(III) O > Ti(IV) O. Hence, in situ growth of amorphous Ti O subcompounds with rich oxygen defects based on Ti₃C₂T_x-MXene is developed. Meanwhile, the composite presents expanded MXene interlayer spacing and much enhanced conductivity. The synergistic effect of enhanced electron/ion conduction gives a high capacity of 107 mAh g⁻¹ at 50 A g⁻¹, which gives 50% and 150% increasements compared with one counterpart without valence adjustment and another one without MXene expansion. It only needs 20 s (at 30 A g⁻¹) to complete the discharge/charge process and obtains a capacity of 144.5 mAh g⁻¹, which also shows a long-term cycling stability at quick-charge mode (121 mAh g⁻¹ after 10000 cycles at 10 A g⁻¹). The enhanced performance comes from fast electron transfer among Ti O subcompounds contributed by rich-defect amorphous TiO_2–x, and a reversible change of elastic MXene with interlayer spacing between 1.4 and 1.9 nm during Na⁺ insertion/extraction process. This study provides a feasible route to boost the kinetics and develop quick-charge sodium-ion battery.     

Fe2VO4 Nanoparticles Anchored on Ordered Mesoporous Carbon with Pseudocapacitive Behaviors for Efficient Sodium Storage

Iron vanadates are attractive anode materials for sodium-ion batteries (SIBs) because of their abundant resource reserves and high capacities. However, their practical application is restricted by the aggregation of materials, sluggish reaction kinetics, and inferior reversibility. Herein, Fe₂VO₄ nanoparticles are anchored on the ordered mesoporous carbon (CMK-3) nanorods to assemble 3D Fe₂VO₄@CMK-3 composites, by solvothermal treatment and subsequent calcination. The resulting composites provide abundant active sites, high electrical conductivity, and excellent structural integrity. The pseudocapacitive-controlled behavior is the dominating sodium storage mechanism, which facilitates a fast charge/discharge process. The Fe₂VO₄@CMK-3 composites exhibit stable sodium-ion storage (219 mAh g⁻¹ under 100 mA g⁻¹ after 300 cycles), good rate performance (144 mAh g⁻¹ at 3.2 A g⁻¹), and excellent cycling performance (132 mAh g⁻¹ at 1 A g⁻¹ with capacity retention of 96.4% after 800 cycles). When coupled with a NaNi_1/3Fe_1/3Mn_1/3O₂ cathode, the sodium-ion full cell displays excellent cycling stability (94 mAh g⁻¹ after 500 cycles at 500 mA g⁻¹). These findings point to the potential of Fe₂VO₄@CMK-3 for application as anodes in SIBs.     

Synergistic Effect between S and Se Enhancing the Electrochemical Behavior of SexSy in Aqueous Zn Metal Batteries

Developing high-capacity conversional cathode materials for aqueous Zn batteries is promising to improve their energy densities but challenging as well. In this work, three kinds of selenium–sulfur solid solutions and their composites (denoted as SeS₁₄ @ 3D-NPCF, SeS_5.76 @ 3D-NPCF, and SeS_2.46 @ 3D-NPCF) are proposed and systematically investigated. Due to the introduction of Se and its synergistic effect with S, their physical and electrochemical properties are manipulated; in particular, by optimizing the Se content in these composites, SeS_5.76 @ 3D-NPCF shows a capacity of 1222 mAh g⁻¹ and flat plateau of 0.71 V at 0.2 A g⁻¹, reaching an ultrahigh energy density of 867.6 Wh kg⁻¹ (based on SeS_5.76), superior rate capacity of 713 mAh g⁻¹ at 5 A g⁻¹, and stable cycling of 75% capacity retention after 500 cycles. In addition, the Zn storage kinetics is determined by the discharge process, during which SeS_5.76 @ 3D-NPCF is converted into ZnSe and ZnS. More importantly, theoretical calculations reveal that Se can tailor the electron density difference, band structure, and reaction energy of S, which increase its conductivity and reactivity to facilitate the electrochemical reaction with Zn. This work explores high performance conversional cathode materials for aqueous Zn metal batteries and presents an effective strategy to modify their intrinsic properties.     

Stabilizing Redox-Active Hexaazatriphenylene in a 2D Conductive Metal–Organic Framework for Improved Lithium Storage Performance

Organic redox-active materials are promising electrode candidates for lithium-ion batteries by virtue of their designable structure and cost-effectiveness. However, their poor electrical conductivity and high solubility in organic electrolytes limit the device's performance and practical applications. Herein, the π-conjugated nitrogen-containing heteroaromatic molecule hexaazatriphenylene (HATN) is strategically embedded with redox-active centers in the skeleton of a Cu-based 2D conductive metal–organic framework (2D c-MOF) to optimize the lithium (Li) storage performance of organic electrodes, which delivers improved specific capacity (763 mAh g⁻¹ at 300 mA g⁻¹), long-term cycling stability (≈90% capacity retention after 600 cycles at 300 mA g⁻¹), and excellent rate performance. The correlation of experimental and computational results confirms that this high Li storage performance derives from the maximum number of active sites (CN sites in the HATN unit and CO sites in the CuO₄ unit), favorable electrical conductivity, and efficient mass transfer channels. This strategy of integrating multiple redox-active moieties into the 2D c-MOF opens up a new avenue for the design of high-performance electrode materials.     

Hierarchical Design of Cross-Linked NiCo2S4 Nanowires Bridged NiCo-Hydrocarbonate Polyhedrons for High-Performance Asymmetric Supercapacitor

Engineering core-shell materials with rationally designed architectures and components is an effective strategy to fulfill the high-performance requirements of supercapacitors. Herein, hierarchical candied-haws-like NiCo₂S₄@NiCo(HCO₃)₂ core-shell heterostructure (NiCo₂S₄@HCs) is designed with NiCo(HCO₃)₂ polyhedrons being tightly strung by cross-linked NiCo₂S₄ nanowires. This rational design not only creates more electroactive sites but also suppresses the volume expansion during the charge–discharge processes. Meanwhile, density functional theory calculations ascertain that the formation of NiCo₂S₄@HCs heterostructure simultaneously facilitates OH⁻ adsorption/desorption and accelerates electron transfer within the electrode, boosting fast and efficient redox reactions. Ex situ X-ray diffraction and Raman measurements reveal that gradual phase transformations from NiCo(HCO₃)₂ to NiCo(OH)₂CO₃ and then to highly-active NiCoOOH take place during the cycles. Therefore, NiCo₂S₄@HCs demonstrates an ultrahigh capacitance of 3178.2 F g⁻¹ at 1 A g⁻¹ and a remarkable rate capability of 2179.3 F g⁻¹ at 30 A g⁻¹. In addition, the asymmetric supercapacitor NiCo₂S₄@HCs//AC exhibits a high energy density of 69.6 W h kg⁻¹ at the power density of 847 W kg⁻¹ and excellent cycling stability with 90.2% retained capacitance after 10 000 cycles. Therefore, this novel structural design has effectively manipulated the interface charge states and guaranteed the structural integrity of electrode materials to achieve superior electrochemical performances.     

In Situ Synthesis of Graphene-Coated Silicon Monoxide Anodes from Coal-Derived Humic Acid for High-Performance Lithium-Ion Batteries

Silicon monoxide (SiO) is attaining extensive interest amongst silicon-based materials due to its high capacity and long cycle life; however, its low intrinsic electrical conductivity and poor coulombic efficiency strictly limit its commercial applications. Here low-cost coal-derived humic acid is used as a feedstock to synthesize in situ graphene-coated disproportionated SiO (D-SiO@G) anode with a facile method. HR-TEM and XRD confirm the well-coated graphene layers on a SiO surface. Scanning transmission X-ray microscopy and X-ray absorption near-edge structure spectra analysis indicate that the graphene coating effectively hinders the side-reactions between the electrolyte and SiO particles. As a result, the D-SiO@G anode presents an initial discharge capacity of 1937.6 mAh g⁻¹ at 0.1 A g⁻¹ and an initial coulombic efficiency of 78.2%. High reversible capacity (1023 mAh g⁻¹ at 2.0 A g⁻¹), excellent cycling performance (72.4% capacity retention after 500 cycles at 2.0 A g⁻¹), and rate capability (774 mAh g⁻¹ at 5 A g⁻¹) results are substantial. Full coin cells assembled with LiFePO₄ electrodes and D-SiO@G electrodes display impressive rate performance. These results indicate promising potential for practical use in high-performance lithium-ion batteries.     

Alkali Metal Cations as Charge-Transfer Bridge for Polarization Promoted Solar-to-H2 Conversion

Utilization of spontaneous polarization electric field of ferroelectric materials to realize the spatial separation and fast transfer of photogenerated charges has been regarded as a promising strategy to fabricate highly efficient photocatalysts. Herein, a novel heterostructure is constructed by coupling potassium poly(heptazine imide) (K-PHI) with ferroelectric Ba_xSr_1-xTiO₃ (B_xST) through a facile electrostatic self-assembly strategy. The ionic species of K-PHI can neutralize the polarized charges in B_xST to form intimate interfacial contact, substantially boosting the internal electric field. Notably, K⁺ cations intercalated into K-PHI act as charge-transfer bridge to promote migration and separation of photogenerated charge carriers. As a result, a significantly improved H₂-evolution rate of 1087.4 µmol h⁻¹ g⁻¹ with an apparent quantum yield (AQY) of 8.05% at 420 nm is achieved over 5% K-PHI/B_0.8ST, standing among the best polymeric carbon nitride-based photocatalysts reported up to date. Moreover, the extreme stability of the catalysts is evidenced by remaining outstanding catalytic performance even after storage for half a year. This strategy can be extended to other alkali metal (Na⁺ and Cs⁺) modified polymeric materials, highlighting the key role of the bridging ions in constructing polarized heterostructure, which sheds light on the design of ferroelectric-assisted photocatalysts.     

Modified Solid Electrolyte Interphases with Alkali Chloride Additives for Aluminum–Sulfur Batteries with Enhanced Cyclability

Aluminum–sulfur batteries employing high-capacity and low-cost electrode materials, as well as non-flammable electrolytes, are promising energy storage devices. However, the fast capacity fading due to the shuttle effect of polysulfides limits their further application. Herein, alkaline chlorides, for example, LiCl, NaCl, and KCl are proposed as electrolyte additives for promoting the cyclability of aluminum–sulfur batteries. Using NaCl as a model additive, it is demonstrated that its addition leads to the formation of a thicker, Na_xAl_yO₂-containing solid electrolyte interphase on the aluminum metal anode (AMA) reducing the deposition of polysulfides. As a result, a specific discharge capacity of 473 mAh g⁻¹ is delivered in an aluminum–sulfur battery with NaCl-containing electrolyte after 50 dis-/charge cycles at 100 mA g⁻¹. In contrast, the additive-free electrolyte only leads to a specific capacity of 313 mAh g⁻¹ after 50 cycles under the same conditions. A similar result is also observed with LiCl and KCl additives. When a KCl-containing electrolyte is employed, the capacity increases to 496 mA h g⁻¹ can be achieved after 100 cycles at 50 mA g⁻¹. The proposed additive strategy and the insight into the solid electrolyte interphase are beneficial for the further development of long-life aluminum–sulfur batteries.     

A Conductive 2D Conjugated Tetrathia[8]circulene-Based Nickel Metal–Organic Framework for Energy Storage

Herein, a novel D₄ symmetrical redox-active ligand tetrathia[8]circulene-2,3,5,6,8,9,11,12-octaol (8OH-TTC) is designed and synthesized, which coordinates with Ni²⁺ ions to construct a 2D conductive metal-organic framework (2D c-MOF) named Ni-TTC. Ni-TTC exhibits typical semiconducting properties with electrical conductivity up to ≈1.0 S m⁻¹ at 298 K. Furthermore, magnetism measurements show the paramagnetic property of Ni-TTC with strong antiferromagnetic coupling due to the presence of semiquinone ligand radicals and Ni²⁺ sites. In virtue of its decent electrical conductivity and good redox activity, the gravimetric capacitance of Ni-TTC is up to 249 F g⁻¹ at a discharge rate of 0.2 A g⁻¹, which demonstrates the potential of tetrathia[8]circulene-based redox-active 2D c-MOFs in energy storage applications.     

Supercritical CO2-Assisted SiOx/Carbon Multi-Layer Coating on Si Anode for Lithium-Ion Batteries

Supercritical CO₂ (SCCO₂), characterized by gas-like diffusivity, low surface tension, and excellent mass transfer properties, is applied to create a SiO_x/carbon multi-layer coating on Si particles. Interaction of SCCO₂ with Si produces a continuous SiO_x layer, which can buffer Si volume change during lithiation/delithiation. In addition, a conformal carbon film is deposited around the Si@SiO_x core. Compared to the carbon film produced via a conventional wet-chemical method, the SCCO₂-deposited carbon has significantly fewer oxygen-containing functional groups and thus higher electronic conductivity. Three types of carbon precursors, namely, glucose, sucrose, and citric acid, in the SCCO₂ syntheses are compared. An eco-friendly, cost-effective, and scalable SCCO₂ process is thus developed for the single-step production of a unique Si@SiO_x@C anode for Li-ion batteries. The sample prepared using the glucose precursor shows the highest tap density, the lowest charge transfer resistance, and the best Li⁺ transport kinetics among the electrodes, resulting in a high specific capacity of 918 mAh g⁻¹ at 5 A g⁻¹. After 300 charge–discharge cycles, the electrode retains its integrity and the accumulation of the solid electrolyte interphase is low. The great potential of the proposed SCCO₂ synthesis and composite anode for Li-ion battery applications is demonstrated.     

Exceeding Theoretical Capacity in Exfoliated Ultrathin Manganese Ferrite Nanosheets via Galvanic Replacement-Derived Self-Hybridization for Fast Rechargeable Lithium-Ion Batteries

Mixed transition metal oxides are promising anodes to meet high-performance energy storage materials; however, their widespread uses are restrained owing to limited theoretical capacity, restricted synthesis methods and templates, low conductivity, and extreme volume expansion. Here, Mn_3-xFe_xO₄ nanosheets with interconnected conductive networks are synthesized via a novel self-hybridization approach of a facile, galvanic replacement-derived, tetraethyl orthosilicate-assisted hydrothermal process. An exceptionally high reversible capacity of 1492.9 mAh g⁻¹ at 0.1 A g⁻¹ is achieved by producing Li-rich phase through combined synergistic effects of amorphous phases with interface modification design for fully utilizing highly spin-polarized surface capacitance. Furthermore, it is demonstrated that large surface area can effectively facilitate Li-ion kinetics, and the formation of interconnected conductive networks improves the electrical conductivity and structural stability by alleviating volume expansion. This leads to a high rate capability of 412.3 mAh g⁻¹ even at an extremely high current density of 10 A g⁻¹ and stable cyclic stability with a capacity up to 921.9 mAh g⁻¹ at 2 A g⁻¹ after 500 cycles. This study can help to overcome theoretically limited electrochemical properties of conventional metal oxide materials, providing a new insight into the rational design with surface alteration to boost Li-ion storage capacity.     

Defect Strategy-Regulated MoSe2-Modified Self-Supporting Graphene Aerogels Serving as Both Cathode and Interlayer of Lithium-Sulfur Batteries

The severe shuttle effect and the sluggish redox reaction kinetics are the two most urgent issues with lithium-sulfur batteries (LSBs). In this work, Se vacancy-rich molybdenum selenide-modified graphene aerogels are designed to serve as both cathode host (MoSe_2-x@GA/S) and freestanding interlayers (MoSe_2-x@GA) for LSBs. The graphene network-supported binder-free sulfur host maximizes electron conductivity/Li⁺ migration rate and alleviates bulk expansion. The defect-rich MoSe_2-x with sulfiphilic-lithiophilic properties accelerates the nucleation and dissociation of Li₂S, while the insertion of a bifunctional interlayer not only facilitates the adsorption and conversion of polysulfides but also regulates the uniform lithium deposition and inhibit the growth of lithium dendrites. As a result, the assembled MoSe_2-x@GA/S+interlayer electrode obtains good feedback in terms of capacity enhancement and cycling stability, possessing a high initial discharge capacity of 1256.9 mA h g⁻¹ at 0.2 C and a slow decay ratio of 0.024% per cycle at a high current density of 1 C after 1000 long-term cycling, and achieve high specific capacity (720.6 mA h g⁻¹) at high sulfur loading (4.8 mg cm⁻²) and lean electrolyte (5.5 µL mg⁻¹) conditions. This insightful work contributes new ideas for the design of binder-free sulfur host and the application of defective electrocatalytic engineering.     

Novel Designed MnS-MoS2 Heterostructure for Fast and Stable Li/Na Storage:Insights into the Advanced Mechanism Attributed to Phase Engineering

Combining 2D MoS₂ with other transition metal sulfide is a promising strategy to elevate its electrochemical performances. Herein, heterostructures constructed using MnS nanoparticles embedded in MoS₂ nanosheets (denoted as MnS-MoS₂) are designed and synthesized as anode materials for lithium/sodium-ion batteries via a facile one-step hydrothermal method. Phase transition and built-in electric field brought by the heterostructure enhance the Li/Na ion intercalation kinetics, elevate the charge transport, and accommodate the volume expansion. The sequential phase transitions from 2H to 3R of MoS₂ and α to γ of MnS are revealed for the first time. As a result, the MnS-MoS₂ electrode delivers outstanding specific capacity (1246.2 mAh g⁻¹ at 1 A g⁻¹), excellent rate, and stable long-term cycling stability (397.2 mAh g⁻¹ maintained after 3000 cycles at 20 A g⁻¹) in Li-ion half-cells. Superior cycling and rate performance are also presented in sodium half-cells and Li/Na full cells, demonstrating a promising practical application of the MnS-MoS₂ electrode. This work is anticipated to afford an in-depth comprehension of the heterostructure contribution in energy storage and illuminate a new perspective to construct binary transition metal sulfide anodes.     

A General Route for Encapsulating Monodispersed Transition Metal Phosphides into Carbon Multi-Chambers toward High-Efficient Lithium-Ion Storage with Underlying Mechanism Exploration

Transition metal phosphides (MP_x) with high theoretical capacities and low cost are regarded as the most promising anodes for lithium-ion batteries (LIBs), but the large volume variations and sluggish kinetics largely restrict their development. To solve the above challenges, herein a generic but effective method is proposed to encapsulate various monodispersed MP_x into flexible carbon multi-chambers (MP_x@NC, MNi, Fe, Co, and Cu, etc.) with pre-reserved voids, working as anodes for LIBs and markedly boosting the Li⁺ storage performance. Ni₂P@NC, one representative example of MP_x@NC anode, shows high reversible capacity (613 mAh g⁻¹, 200 cycles at 0.2 A g⁻¹), and superior cycle stability (475 mAh g⁻¹, 800 cycles at 2 A g⁻¹). Full cell coupled with LiFePO₄ displays a high reversible capacity (150.1 mAh g⁻¹ at 0.1 A g⁻¹) with stable cycling performance. In situ X-ray diffraction and transmission electron microscope techniques confirm the reversible conversion reaction mechanism and robust structural integrity, accounting for enhanced rate and cycling performance. Theoretical calculations reveal the synergistic effect between MP_x and carbon shells, which can significantly promote electron transfer and reduce diffusion energy barriers, paving ways to design high-energy-density materials for energy storage systems.     

Ultralong Cycle Life for Deep Potassium Storage Enabled by BiOCl/MXene van der Waals Heterostructures

Conversion/alloying-type anodes are drawing attention due to their high theoretical capacities, but inferior reversibility, especially under low current densities, has hampered potential applications. Conventional strategies mainly focus on conversion/alloying processes, whereas the intercalation process is rarely analyzed. Herein, the intercalation process is correlated with conversion/alloying processes by ion dispersion states. BiOCl/Ti₃C₂T_x MXene van der Waals heterostructure is selected as a proof-of-concept system. Multifunctional MXenes not only contribute to atomic dispersion and boosted ion diffusion at the first cycle by constructing a novel heterostructure but serve as supporting frameworks to sustain long-term structural stability. Consequently, a cell with BiOCl/MXene anode delivers an ultralong cycle-life of running over ten months, maintaining a high capacity of 225 mAh g⁻¹ over 1300 cycles at 100 mA g⁻¹ and a retention of 81.3%. These findings verify that enhanced initial intercalation can facilitate higher reversibility and shed light on developing high-performance conversion/alloying-type anodes.     

Boosting Zn2+ and NH4+ Storage in Aqueous Media via In-Situ Electrochemical Induced VS2/VOx Heterostructures

Aqueous-ion batteries have received much attention owing to the merits of high safety, low cost, and environmental friendliness. Among potential cathode candidates, transition metal sulfides drew little attention since they suffer from low capacity, low working potential, and fast capacity fading. Here, advantage is taken of the chemical instability of VS₂ in aqueous electrolyte to in situ fabricate a heterostructural VS₂/VO_x material. Benefiting from the internal electric field at heterointerfaces, high conductivity of vanadium sulfide and high chemical stability of vanadium oxides, heterostructural VS₂/VO_x delivers an enhanced working potential by 0.25 V, superior rate capability with specific capacity of 156 mA h g⁻¹ at 10 A g⁻¹, and long-term stability over 3000 cycles as Zn²⁺ storage electrode. In addition, heterostructural VS₂/VO_x is employed as the cathode for aqueous NH₄⁺ ion storage with high reversible capacity over 150 mA h g⁻¹ and long lifespan over 1000 cycles, surpassing the state-of-the-art materials. VS₂/VO_x is proved to demonstrate a (de)intercalation process for Zn²⁺ storage, while a conversion reaction accompanied by insertion is responsible for nonmetal NH₄⁺. The strong insight obtained in this study sheds light on a new methodology of exploring the potential of transition metal sulfides-based cathode materials for aqueous ion batteries.     

Tailoring Ultrahigh Energy Density and Stable Dendrite-Free Flexible Anode with Ti3C2Tx MXene Nanosheets and Hydrated Ammonium Vanadate Nanobelts for Aqueous Rocking-Chair Zinc Ion Batteries

Exploiting Zn metal-free anode materials would be an effective strategy to resolve the problems of Zn metal dendrites that severely hinder the development of Zn ion batteries (ZIBs). However, the study of Zn metal-free anode materials is still in their infancy, and more importantly, the low energy density severely limits their practical implementations. Herein, a novel (NH₄)₂V₁₀O₂₅ · 8H₂O@Ti₃C₂T_x (NHVO@Ti₃C₂T_x) film anode is proposed and investigated for constructing “rocking-chair” ZIBs. The NHVO@Ti₃C₂T_x electrode shows a capacity of 514.7 mAh g⁻¹ and presents low potential which is 0.59 V (vs Zn²⁺/Zn) at 0.1 A g⁻¹. The introduction of Ti₃C₂T_x not only affords an interconnected conductive network, but also stabilizes the NHVO nanobelts structure for a long cycle life (84.2% retention at 5.0 A g⁻¹ over 6000 cycles). As a proof-of-concept, a zinc metal-free full battery is successfully demonstrated, which delivers the highest capacity of 131.7 mAh g⁻¹ (mass containing anodic and cathodic) and energy density of 97.1 Wh kg⁻¹ compared to all reported aqueous “rocking-chair” ZIBs. Furthermore, a long cycling span of 6000 cycles is obtained with capacity retention reaching up to 92.1%, which is impressive. This work is expected to provide new moment toward V-based materials for “rocking-chair” ZIBs.