A Layered Inorganic–Organic Open Framework Material as a 4 V Positive Electrode with High‐Rate Performance for K‐Ion Batteries

K‐ion batteries (KIBs) are promising for large‐scale energy storage owing to various advantages like the high abundance of potassium resources in the Earth's crust, high operational potentials, and high power due to fast diffusion of K⁺ ions. However, to realize the practical application of KIBs, electrode materials are needed with high operational voltage, good capacity, long cycle life, and low‐cost. This work reports a layered open framework material, K₂[(VOHPO₄)₂(C₂O₄)], composited with reduced graphene oxide (rGO) as a 4 V positive electrode material for KIBs. The material is prepared by a simple precipitation reaction at room temperature. The material demonstrates reversible K‐extraction/insertion with conventional carbonate ester KPF₆ solutions; however, with low specific capacity and low Coulombic efficiency. A high discharge capacity of >100 mAh g^?1 with good cycling stability and higher Coulombic efficiency is achieved in a highly concentrated electrolyte, 7 mol kg^?1 of potassium bis(fluorosulfonyl)amide (KFSA) in dimethoxyethane (DME) at 0.1 C rate. Due to the facile migration of K⁺ ions in the framework, the material exhibits excellent rate capability with a discharge capacity of 80 mAh g^?1 at 10 C rate, and a good capacity retention of 67% after 500 cycles at 2 C rate.     

Unlocking Few‐Layered Ternary Chalcogenides for High‐Performance Potassium‐Ion Storage

Potassium‐ion batteries (KIBs) have attracted increasing attention for grid‐scale energy storage due to the abundance of potassium resources, low cost, and competitive energy density. The key challenge for KIBs is to develop high‐performance electrode materials. However, the exploration of high‐capacity and ultrastable electrodes for KIBs remains challenging because of the sluggish diffusion kinetics of K⁺ ions during the charging/discharging processes. This study reports for the first time a facile ion‐intercalation‐mediated exfoliation method with Mg²⁺ cations and NO₃^– anions as ion assistants for the fabrication of expanded few‐layered ternary Ta₂NiSe₅ (EF‐TNS) flakes with interlayer spacing up to 1.1 nm and abundant Se sites (NiSe₄ tetrahedra/TaSe₆ octahedra clusters) for superior potassium‐ion storage. The EF‐TNS deliver a high capacity of 315 mAh g^–1, excellent rate capability (121 mAh g^–1 at a current density of 1000 mA g^–1), and ultrastable cycling performance (81.4% capacity retention after 1100 cycles). Detailed theoretical analysis via first‐principles calculations and experimental results elucidate that K⁺ ions intercalate through the expanded interlayers effectively and prefer to transport along zigzag pathways in layered Ta₂NiSe₅. This work provides a new avenue for designing novel ternary intercalation/pseudocapacitance‐type KIBs with high capacity, excellent rate capability, and superior long‐term cycling performance.     

Partially Reduced Holey Graphene Oxide as High Performance Anode for Sodium‐Ion Batteries

The current Na⁺ storage performance of carbon‐based materials is still hindered by the sluggish Na⁺ ion transfer kinetics and low capacity. Graphene and its derivatives have been widely investigated as electrode materials in energy storage and conversion systems. However, as anode materials for sodium‐ion batteries (SIBs), the severe π–π restacking of graphene sheets usually results in compact structure with a small interlayer distance and a long ion transfer distance, thus leading to low capacity and poor rate capability. Herein, partially reduced holey graphene oxide is prepared by simple H₂O₂ treatment and subsequent low temperature reduction of graphene oxide, leading to large interlayer distance (0.434 nm), fast ion transport, and larger Na⁺ storage space. The partially remaining oxygenous groups can also contribute to the capacity by redox reaction. As anode material for SIBs, the optimized electrode delivers high reversible capacity, high rate capability (365 and 131 mAh g^?1 at 0.1 and 10 A g^?1, respectively), and good cycling performance (163 mAh g^?1 after 3000 cycles at a current density of 2 A g^?1), which is among the best reported performances for carbon‐based SIB anodes.     

Mesoporous MoS2 as a Transition Metal Dichalcogenide Exhibiting Pseudocapacitive Li and Na‐Ion Charge Storage

The ion insertion properties of MoS₂ continue to be of widespread interest for energy storage. While much of the current work on MoS₂ has been focused on the high capacity four‐electron reduction reaction, this process is prone to poor reversibility. Traditional ion intercalation reactions are highlighted and it is demonstrated that ordered mesoporous thin films of MoS₂ can be utilized as a pseudocapacitive energy storage material with a specific capacity of 173 mAh g^?1 for Li‐ions and 118 mAh g^?1 for Na‐ions at 1 mV s^?1. Utilizing synchrotron grazing incidence X‐ray diffraction techniques, fast electrochemical kinetics are correlated with the ordered porous structure and with an iso‐oriented crystal structure. When Li‐ions are utilized, the material can be charged and discharged in 20 seconds while still achieving a specific capacity of 140 mAh g^?1. Moreover, the nanoscale architecture of mesoporous MoS₂ retains this level of lithium capacity for 10 000 cycles. A detailed electrochemical kinetic analysis indicates that energy storage for both ions in MoS₂ is due to a pseudocapacitive mechanism.     

Confined Fe2VO4⊂Nitrogen‐Doped Carbon Nanowires with Internal Void Space for High‐Rate and Ultrastable Potassium‐Ion Storage

Developing low‐cost, high‐capacity, high‐rate, and robust earth‐abundant electrode materials for energy storage is critical for the practical and scalable application of advanced battery technologies. Herein, the first example of synthesizing 1D peapod‐like bimetallic Fe₂VO₄ nanorods confined in N‐doped carbon porous nanowires with internal void space (Fe₂VO₄?NC nanopeapods) as a high‐capacity and stable anode material for potassium‐ion batteries (KIBs) is reported. The peapod‐like Fe₂VO₄?NC nanopeapod heterostructures with interior void space and external carbon shell efficiently prevent the aggregation of the active materials, facilitate fast transportation of electrons and ions, and accommodate volume variation during the cycling process, which substantially boosts the rate and cycling performance of Fe₂VO₄. The Fe₂VO₄?NC electrode exhibits high reversible specific depotassiation capacity of 380 mAh g^?1 at 100 mA g^?1 after 60 cycles and remarkable rate capability as well as long cycling stability with a high capacity of 196 mAh g^?1 at 4 A g^?1 after 2300 cycles. The first‐principles calculations reveal that Fe₂VO₄?NC nanopeapods have high ionic/electronic conductivity characteristics and low diffusion barriers for K⁺‐intercalation. This study opens up new way for investigating high‐capacity metal oxide as high‐rate and robust electrode materials for KIBs.     

One‐Step Synthesis of 2‐Ethylhexylamine Pillared Vanadium Disulfide Nanoflowers with Ultralarge Interlayer Spacing for High‐Performance Magnesium Storage

Rechargeable magnesium batteries (RMBs) are attractive candidates for large‐scale energy storage owing to the high theoretical specific capacity, rich earth abundance, and good safety characteristics. However, the development of desirable cathode materials for RMBs is constrained by the high polarity and slow intercalation kinetics of Mg²⁺ ions. Herein, it is demonstrated that 2‐ethylhexylamine pillared vanadium disulfide nanoflowers (expanded VS₂) with enlarged interlayer distances exhibit greatly boosted electrochemical performance as a cathode material in RMBs. Through a one‐step solution‐phase synthesis and in situ 2‐ethylhexylamine intercalation process, VS₂ nanoflowers with ultralarge interlayer spacing are prepared. A series of ex situ characterizations verify that the cathode of expanded VS₂ nanoflowers undergoes a reversible intercalation reaction mechanism, followed by a conversion reaction mechanism. Electrochemical kinetics analysis reveal a relatively fast Mg‐ion diffusivity of expanded VS₂ nanoflowers in the order of 10^?11–10^?12 cm² s^?1, and the pseudocapacitive contribution is up to 64% for the total capacity at 1 mV s^?1. The expanded VS₂ nanoflowers show highly reversible discharge capacity (245 mAh g^?1 at 100 mA g^?1), good rate capability (103 mAh g^?1 at 2000 mA g^?1), and stable cycling performance (90 mAh g^?1 after 600 cycles at 1000 mA g^?1).     

Nature of FeSe2/N‐C Anode for High Performance Potassium Ion Hybrid Capacitor

Potassium ion hybrid capacitors have great potential for large‐scale energy devices, because of the high power density and low cost. However, their practical applications are hindered by their low energy density, as well as electrolyte decomposition and collector corrosion at high potential in potassium bis(fluoro‐sulfonyl)imide‐based electrolyte. Therefore, anode materials with high capacity, a suitable voltage platform, and stability become a key factor. Here, N‐doping carbon‐coated FeSe₂ clusters are demonstrated as the anode material for a hybrid capacitor, delivering a reversible capacity of 295 mAh g^?1 at 100 mA g^?1 over 100 cycles and a high rate capability of 158 mAh g^?1 at 2000 mA g^?1 over 2000 cycles. Meanwhile, through density functional theory calculations, in situ X‐ray diffraction, and ex situ transmission electron microscopy, the evolution of FeSe₂ to Fe₃Se₄ for the electrochemical reaction mechanism is successfully revealed. The battery‐supercapacitor hybrid using commercial activated carbon as the cathode and FeSe₂/N‐C as the anode is obtained. It delivers a high energy density of 230 Wh kg^?1 and a power density of 920 W kg^?1 (the energy density and power density are calculated based on the total mass of active materials in the anode and cathode).     

MoS2/Graphene Nanosheets from Commercial Bulky MoS2 and Graphite as Anode Materials for High Rate Sodium‐Ion Batteries

Tuning heterointerfaces between hybrid phases is a very promising strategy for designing advanced energy storage materials. Herein, a low‐cost, high‐yield, and scalable two‐step approach is reported to prepare a new type of hybrid material containing MoS₂/graphene nanosheets prepared from ball‐milling and exfoliation of commercial bulky MoS₂ and graphite. When tested as an anode material for a sodium‐ion battery, the as‐prepared MoS₂/graphene nanosheets exhibit remarkably high rate capability (284 mA h g^?1 at 20 A g^?1 (≈30C) and 201 mA h g^?1 at 50 A g^?1 (≈75C)) and excellent cycling stability (capacity retention of 95% after 250 cycles at 0.3 A g^?1). Detailed experimental measurements and density functional theory calculation reveal that the functional groups in 2D MoS₂/graphene heterostructures can be well tuned. The impressive rate capacity of the as‐prepared MoS₂/graphene hybrids should be attributed to the heterostructures with a low degree of defects and residual oxygen containing groups in graphene, which subsequently improve the electronic conductivity of graphene and decrease the Na⁺ diffusion barrier at the MoS₂/graphene interfaces in comparison with the acid treated one.     

High Capacity Adsorption—Dominated Potassium and Sodium Ion Storage in Activated Crumpled Graphene

Structurally and chemically defective activated‐crumbled graphene (A‐CG) is employed to achieve unique synergy of large reversible potassium (K) and sodium (Na) ion storage capacity with fast charging and extended cyclability. A‐CG synthesis consists of low temperature spraying of graphene oxide slurry, followed by partial reduction annealing and air activation. For K storage, the reversible capacities are 340 mAh g^?1 at 0.04 A g^?1, 261 mAh g^?1 at 0.5 A g^?1, and 210 mAh g^?1 at 2 A g^?1. For Na storage, the reversible capacities are 280 mAh g^?1 at 0.04 A g^?1, 191 mAh g^?1 at 0.5 A g^?1, and 151 mAh g^?1 at 2 A g^?1. A‐CG shows a stable intermediate rate (0.5 Ag^?1) cycling with both K and Na, with minimal fade after 2800 and 8000 cycles. These are among the most favorable capacity—rate capability—cyclability combinations recorded for potassium‐ion battery and sodium‐ion battery carbons. Electroanalytical studies (cyclic voltammetry, galvanostatic intermittent titration technique, b‐value) and density functional theory (DFT) reveal that enhanced electrochemical performance originates from ion adsorption at various defects, such as Stone–Wales defects. Moreover, DFT highlights enhanced thermodynamic stability of A‐CG with adsorbed K versus with adsorbed Na, explaining the unexpected higher reversible capacity with the former.     

Ion Transport Nanotube Assembled with Vertically Aligned Metallic MoS2 for High Rate Lithium‐Ion Batteries

Metallic phase molybdenum disulfide (MoS₂) is well known for orders of magnitude higher conductivity than 2H semiconducting phase MoS₂. Herein, for the first time, the authors design and fabricate a novel porous nanotube assembled with vertically aligned metallic MoS₂ nanosheets by using the scalable solvothermal method. This metallic nanotube has the following advantages: (i) intrinsic high electrical conductivity that promotes the rate performance of battery and eliminates the using of conductive additive; (ii) hierarchical, hollow, porous, and aligned structure that assists the electrolyte transportation and diffusion; (iii) tubular structure that avoids restacking of 2D nanosheets, and therefore maintains the electrochemistry cycling stability; and (iv) a shortened ion diffusion path, that improves the rate performance. This 1D metallic MoS₂ nanotube is demonstrated to be a promising anode material for lithium‐ion batteries. The unique structure delivers an excellent reversible capacity of 1100 mA h g^?1 under a current density of 5 A g^?1 after 350 cycles, and an outstanding rate performance of 589 mA h g^?1 at a current density of 20 A g^?1. Furthermore, attributed to the material's metallic properties, the electrode comprising 100% pure material without any additive provides an ideal system for the fundamental electrochemical study of metallic MoS₂. This study first reveals the characteristic anodic peak at 1.5 V in cyclic voltammetry of metallic MoS_2. This research sheds light on the fabrication of metallic 1D, 2D, or even 3D structures with 2D nanosheets as building blocks for various applications.     

Vertically Oriented MoS2 with Spatially Controlled Geometry on Nitrogenous Graphene Sheets for High‐Performance Sodium‐Ion Batteries

Inspired by the great success of graphite in lithium‐ion batteries, anode materials that undergo an intercalation mechanism are considered to provide stable and reversible electrochemical sodium‐ion storage for sodium‐ion battery (SIB) applications. Though MoS₂ is a promising 2D material for SIBs, it suffers from deformation of its layered structure during repeated intercalation of Na⁺, resulting in undesirable electrochemical behaviors. In this study, vertically oriented MoS₂ on nitrogenous reduced graphene oxide sheets (VO‐MoS₂/N‐RGO) is presented with designed spatial geometries, including sheet density and height, which can deliver a remarkably high reversible capacity of 255 mA h g^?1 at a current density of 0.2 A g^?1 and 245 mA h g^?1 at a current density of 1 A g^?1, with a total fluctuation of 5.35% over 1300 cycles. These results are superior to those obtained with well‐developed hard carbon structures. Furthermore, a SIB full cell composed of the optimized VO‐MoS₂/N‐RGO anode and a Na₂V₃(PO₄)₃ cathode reaches a specific capacity of 262 mA h g^?1 (based on the anode mass) during 50 cycles, with an operated voltage range of 2.4 V, demonstrating the potentially rewarding SIB performance, which is useful for further battery development.     

A Novel Graphene Oxide Wrapped Na2Fe2(SO4)3/C Cathode Composite for Long Life and High Energy Density Sodium‐Ion Batteries

The cathode materials in the Na‐ion battery system are always the key issue obstructing wider application because of their relatively low specific capacity and low energy density. A graphene oxide (GO) wrapped composite, Na₂Fe₂(SO₄)₃@C@GO, is fabricated via a simple freeze‐drying method. The as‐prepared material can deliver a 3.8 V platform with discharge capacity of 107.9 mAh g^?1 at 0.1 C (1 C = 120 mA g^?1) as well as offering capacity retention above 90% at a discharge rate of 0.2 C after 300 cycles. The well‐constructed carbon network provides fast electron transfer rates, and thus, higher power density also can be achieved (75.1 mAh g^?1 at 10 C). The interface contribution of GO and Na₂Fe₂(SO₄)₃ is recognized and studied via density function theory calculation. The Na storage mechanism is also investigated through in situ synchrotron X‐ray diffraction, and pseudocapacitance contributions are also demonstrated. The diffusion coefficient of Na⁺ ions is around 10^?12–10^?10.8 cm² s^?1 during cycling. The higher working voltage of this composite is mainly ascribed to the larger electronegativity of the element S. The research indicates that this well‐constructed composite would be a competitive candidate as a cathode material for Na‐ion batteries.     

Amorphous MoS3 Infiltrated with Carbon Nanotubes as an Advanced Anode Material of Sodium‐Ion Batteries with Large Gravimetric,Areal, and Volumetric Capacities

The search for earth‐abundant and high‐performance electrode materials for sodium‐ion batteries represents an important challenge to current battery research. 2D transition metal dichalcogenides, particularly MoS₂, have attracted increasing attention recently, but few of them so far have been able to meet expectations. In this study, it is demonstrated that another phase of molybdenum sulfide—amorphous chain‐like MoS₃—can be a better choice as the anode material of sodium‐ion batteries. Highly compact MoS₃ particles infiltrated with carbon nanotubes are prepared via the facile acid precipitation method in ethylene glycol. Compared to crystalline MoS₂, the resultant amorphous MoS₃ not only exhibits impressive gravimetric performance—featuring excellent specific capacity (≈615 mA h g^?1), rate capability (235 mA h g^?1 at 20 A g^?1), and cycling stability but also shows exceptional volumetric capacity of ≈1000 mA h cm^?3 and an areal capacity of >6.0 mA h cm^?2 at very high areal loadings of active materials (up to 12 mg cm^?2). The experimental results are supported by density functional theory simulations showing that the 1D chains of MoS₃ can facilitate the adsorption and diffusion of Na⁺ ions. At last, it is demonstrated that the MoS₃ anode can be paired with an Na₃V₂(PO₄)₃ cathode to afford full cells with great capacity and cycling performance.     

P2‐K0.75[Ni1/3Mn2/3]O2 Cathode Material for High Power and Long Life Potassium‐Ion Batteries

Rationally designed P2‐K_0.75[Ni_1/3Mn_2/3]O₂ is introduced as a novel cathode material for potassium‐ion batteries (KIBs). P2‐K_0.75[Ni_1/3Mn_2/3]O₂ cathode material designed through electrochemical ion‐exchange from P2‐Na_2/3[Ni_1/3Mn_2/3]O₂ exhibits satisfactory electrode performances; 110 mAh g^?1 (20 mA g^?1) retaining 86% of capacity for 300 cycles and unexpectedly high reversible capacity of about 91 mAh g^?1 (1400 mA g^?1) with excellent capacity retention of 83% over 500 cycles. According to theoretical and experimental investigations, the overall potassium storage mechanism of P2‐K_0.75[Ni_1/3Mn_2/3]O₂ is revealed to be a single‐phase reaction with small lattice change upon charge and discharge, presenting the Ni^4+/2+ redox couple reaction. Such high power capability is possible through the facile K⁺ migration in the K_0.75[Ni_1/3Mn_2/3]O₂ structure with a low activation barrier energy of ≈210 meV. These findings indicate that P2‐K_0.75[Ni_1/3Mn_2/3]O₂ is a promising candidate cathode material for high‐rate and long‐life KIBs.     

Vertically Aligned Sn4+ Preintercalated Ti2CTX MXene Sphere with Enhanced Zn Ion Transportation and Superior Cycle Lifespan

While 2D MXenes have been widely used in energy storage systems, surface barriers induced by restacking of nanosheets and the limited kinetics resulting from insufficient interlayer spacing are two unresolved issues. Here an Sn⁴⁺ preintercalated Ti₂CT_X with effectively enlarged interlayer spacing is synthesized. The preintercalated Ti₂CT_X is aligned on a carbon sphere to further enhance ion transportation by shortening the ion diffusion path and enhancing the reaction kinetics. As a result, when paired with a Zn anode, 12 500 cycles, which equals 2 800 h cycle time, and 5% capacity fluctuation are obtained, surpassing all reported MXene‐based aqueous electrodes. At 0.1 A g^‐1, the capacity reaches 138 mAh g^‐1, and 92 mAh g^‐1 remains even at 5 A g^‐1. In addition, the low anti‐self‐discharge rate of 0.989 mV h^‐1 associated with a high capacity retention of 80.5% over 548 h is obtained. Moreover, the fabricated quasi‐solid capacitor based on a hydrogel film electrolyte exhibits good mechanical deformation and weather resistance. This work employs both preintercalation and alignment to MXene and achieves enhanced ion diffusion kinetics in an aqueous zinc ion capacitors (ZICs) system, which may be applied to other MXene batteries for enhanced performance.     

Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes

Hard carbon (HC) is the state‐of‐the‐art anode material for sodium‐ion batteries (SIBs). However, its performance has been plagued by the limited initial Coulombic efficiency (ICE) and mediocre rate performance. Here, experimental and theoretical studies are combined to demonstrate the application of lithium‐pretreated HC (LPHC) as high‐performance anode materials for SIBs by manipulating the solid electrolyte interphase in tetraglyme (TEGDME)‐based electrolyte. The LPHC in TEGDME can 1) deliver > 92% ICE and ≈220 mAh g^?1 specific capacity, twice of the capacity (≈100 mAh g^?1) in carbonate electrolyte; 2) achieve > 85% capacity retention over 1000 cycles at 1000 mA g^?1 current density (4 C rate, 1 C = 250 mA g^?1) with a specific capacity of ≈150 mAh g^?1, ≈15 times of the capacity (10 mAh g^?1) in carbonate. The full cell of Na₃V₂(PO₄)₃‐LPHC in TEGDME demonstrated close to theoretical specific capacity of ≈98 mAh g^?1 based on Na₃V₂(PO₄)₃ cathode, ≈2.5 times of the value (≈40 mAh g^?1) with nontreated HC. This work provides new perception on the anode development for SIBs.     

Defect‐Rich Soft Carbon Porous Nanosheets for Fast and High‐Capacity Sodium‐Ion Storage

Soft carbon has attracted tremendous attention as an anode in rocking‐chair batteries owing to its exceptional properties including low‐cost, tunable interlayer distance, and favorable electronic conductivity. However, it fails to exhibit decent performance for sodium‐ion storage owing to difficulties in the formation of sodium intercalation compounds. Here, microporous soft carbon nanosheets are developed via a microwave induced exfoliation strategy from a conventional soft carbon compound obtained by pyrolysis of 3,4,9,10‐perylene tetracarboxylic dianhydride. The micropores and defects at the edges synergistically leads to enhanced kinetics and extra sodium‐ion storage sites, which contribute to the capacity increase from 134 to 232 mAh g^?1 and a superior rate capability of 103 mAh g^?1 at 1000 mA g^?1 for sodium‐ion storage. In addition, the capacitance‐dominated sodium‐ion storage mechanism is identified through the kinetics analysis. The in situ X‐ray diffraction analyses are used to reveal that sodium ions intercalate into graphitic layers for the first time. Furthermore, the as‐prepared nanosheets can also function as an outstanding anode for potassium‐ion storage (reversible capacity of 291 mAh g^?1) and dual‐ion full cell (cell‐level capacity of 61 mAh g^?1 and average working voltage of 4.2 V). These properties represent the potential of soft carbon for achieving high‐energy, high‐rate, and low‐cost energy storage systems.     

A Nanosheet Array of Cu2Se Intercalation Compound with Expanded Interlayer Space for Sodium Ion Storage

Intercalation chemistry/engineering has been widely investigated in the development of electrochemical energy storage. Graphite, as an old intercalation host, is receiving vigorous attention again via a new halogen intercalation. Whereas, exploiting new intercalation hosts and optimizing the intercalation effect still remains a great challenge. This study fabricates a Cu₂Se intercalation compound showing expanded interlayer space and nanosheet array features by using a green growth approach, in which cetyltrimethyl ammonium bromide (CTAB) is inserted into Cu₂Se at an ambient temperature. When acting as an electrode material for sodium‐ion batteries, the Cu₂Se–CTAB nanosheet arrays exhibit excellent discharge capacity and rate capability (426.0 mAh g^?1 at 0.1 A g^?1 and 238.1 mAh g^?1 at 30 A g^?1), as well as high capacity retention of ≈90% at 20 A g^?1 after 6500 cycles. Benefiting from the porous array architecture, the transport of electrolytes is facilitated on the surface of Cu₂Se nanosheets. In particular, the CTAB intercalated in the interlayer space of Cu₂Se can increase its buffer space, stabilize the polyselenide shuttle, and prevent the fast growth of Cu nanoparticles during its electrochemical process.     

Novel K3V2(PO4)3/C Bundled Nanowires as Superior Sodium‐Ion Battery Electrode with Ultrahigh Cycling Stability

Sodium‐ion battery has captured much attention due to the abundant sodium resources and potentially low cost. However, it suffers from poor cycling stability and low diffusion coefficient, which seriously limit its widespread application. Here, K₃V₂(PO₄)₃/C bundled nanowires are fabricated usinga facile organic acid‐assisted method. With a highly stable framework, nanoporous structure, and conductive carbon coating, the K₃V₂(PO₄)₃/C bundled nanowires manifest excellent electrochemical performances in sodium‐ion battery. A stable capacity of 119 mAh g^?1 can be achieved at 100 mA g^?1. Even at a high current density of 2000 mA g^?1, 96.0% of the capacity can be retained after 2000 charge–discharge cycles. Comparing with K₃V₂(PO₄)₃/C blocks, the K₃V₂(PO₄)₃/C bundled nanowires show significantly improved cycling stability. This work provides a facile and effective approach to enhance the electrochemical performance of sodium‐ion batteries.     

Pseudocapacitive Charge Storage in Thick Composite MoS2 Nanocrystal‐Based Electrodes

A synthesis methodology is demonstrated to produce MoS₂ nanoparticles with an expanded atomic lamellar structure that are ideal for Faradaic‐based capacitive charge storage. While much of the work on MoS₂ focuses on the high capacity conversion reaction, that process is prone to poor reversibility. The pseudocapacitive intercalation‐based charge storage reaction of MoS₂ is investigated, which is extremely fast and highly reversible. A major challenge in the field of pseudocapacitive‐based energy storage is the development of thick electrodes from nanostructured materials that can sustain the fast inherent kinetics of the active nanocrystalline material. Here a composite electrode comprised of a poly(acrylic acid) binder, carbon fibers, and carbon black additives is utilized. These electrodes deliver a specific capacity of 90 mAh g^?1 in less than 20 s and can be cycled 3000 times while retaining over 80% of the original capacity. Quantitative kinetic analysis indicates that over 80% of the charge storage in these MoS₂ nanocrystals is pseudocapacitive. Asymmetric full cell devices utilizing a MoS₂ nanocrystal‐based electrode and an activated carbon electrode achieve a maximum power density of 5.3 kW kg^?1 (with 6 Wh kg^?1 energy density) and a maximum energy density of 37 Wh kg^?1 (with 74 W kg^?1power density).