Facile Spraying Synthesis and High‐Performance Sodium Storage of Mesoporous MoS2/C Microspheres

A facile one‐step spraying synthesis of MoS₂/C microspheres and their enhanced electrochemical performance as anode of sodium‐ion batteries is reported. An aerosol spraying pyrolysis without any template is employed to synthesize MoS₂/C microspheres, in which ultrathin MoS₂ nanosheets (≈2 nm) with enlarged interlayers (≈0.64 nm) are homogeneously embedded in mesoporous carbon microspheres. The as‐synthesized mesoporous MoS₂/C microspheres with 31 wt% carbon have been applied as an anode material for sodium ion batteries, demonstrating long cycling stability (390 mAh g^?1 after 2500 cycles at 1.0 A g^?1) and high rate capability (312 mAh g^?1 at 10.0 A g^?1 and 244 mAh g^?1 at 20.0 A g^?1). The superior electrochemical performance is due to the uniform distribution of ultrathin MoS₂ nanosheets in mesoporous carbon frameworks. This kind of structure not only effectively improves the electronic and ionic transport through MoS₂/C microspheres, but also minimizes the influence of pulverization and aggregation of MoS₂ nanosheets during repeated sodiation and desodiation.     

General Synthesis of N‐Doped Macroporous Graphene‐Encapsulated Mesoporous Metal Oxides and Their Application as New Anode Materials for Sodium‐Ion Hybrid Supercapacitors

A general method to synthesize mesoporous metal oxide@N‐doped macroporous graphene composite by heat‐treatment of electrostatically co‐assembled amine‐functionalized mesoporous silica/metal oxide composite and graphene oxide, and subsequent silica removal to produce mesoporous metal oxide and N‐doped macroporous graphene simultaneously is reported. Four mesoporous metal oxides (WO_{3? x} , Co₃O₄, Mn₂O₃, and Fe₃O₄) are encapsulated in N‐doped macroporous graphene. Used as an anode material for sodium‐ion hybrid supercapacitors (Na‐HSCs), mesoporous reduced tungsten oxide@N‐doped macroporous graphene (m‐WO_{3? x} @NM‐rGO) gives outstanding rate capability and stable cycle life. Ex situ analyses suggest that the electrochemical reaction mechanism of m‐WO_{3? x} @NM‐rGO is based on Na⁺ intercalation/de‐intercalation. To the best of knowledge, this is the first report on Na⁺ intercalation/de‐intercalation properties of WO_{3? x} and its application to Na‐HSCs.     

Bamboo‐Like Hollow Tubes with MoS2/N‐Doped‐C Interfaces Boost Potassium‐Ion Storage

Potassium‐ion batteries (KIBs) are new‐concept of low‐cost secondary batteries, but the sluggish kinetics and huge volume expansion during cycling, both rooted in the size of large K ions, lead to poor electrochemical behavior. Here, a bamboo‐like MoS₂/N‐doped‐C hollow tubes are presented with an expanded interlayer distance of 10 Å as a high‐capacity and stable anode material for KIBs. The bamboo‐like structure provides gaps along axial direction in addition to inner cylinder hollow space to mitigate the strains in both radial and vertical directions that ultimately leads to a high structural integrity for stable long‐term cycling. Apart from being a constituent of the interstratified structure the N‐doped‐C layers weave a cage to hold the potassiation products (polysulfide and the Mo nanoparticles) together, thereby effectively hindering the continuing growth of solid electrolyte interphase in the interior of particles. The density functional theory calculations prove that the MoS₂/N‐doped‐C atomic interface can provide an additional attraction toward potassium ion. As a result, it delivers a high capacity at a low current density (330 mAh g^?1 at 50 mA g^?1 after 50 cycles) and a high‐capacity retention at a high current density (151 mAh g^?1 at 500 mA g^?1 after 1000 cycles).     

Dual‐Doped Hematite Nanorod Arrays on Carbon Cloth as a Robust and Flexible Sodium Anode

Rechargeable batteries with flexibility can find tremendous applications in wearable and bendable electronics. One central mission for the advancement of such high‐performance batteries is the exploration of flexible anodes with electrochemical and mechanical robustness. Herein reported is a robust and flexible sodium‐ion anode based on self‐supported hematite nanoarray grown on carbon cloth. The ammonia treatment that results in dual doping of both nitrogen and low‐valent iron renders surface reactivity and electric conductivity to the material. The dual‐doped hematite arrays afford a robust activity for sodium storage, exhibiting reversible capacities of 895 and 382 mAh g^?1 at current rates of 0.1 and 5 A g^?1, respectively, or 615 and 356 mAh g^?1 by removing the contribution of the substrate. They also sustain 85% of the initial capacity upon 200 cycles at 0.2 A g^?1. To demonstrate the flexibility, full cells composed of a hematite array anode and Na₃V₂(PO₄)₃/C cathode are assembled. The cell is capable of affording an energy density of 201 Wh kg^?1 and sustaining repeated bending without performance decay, demonstrating a significant potential in practical application.     

A High‐Performance Sodium‐Ion Hybrid Capacitor Constructed by Metal–Organic Framework–Derived Anode and Cathode Materials

Sodium‐ion hybrid capacitors (SIHCs) can potentially combine the virtues of high‐energy density of batteries and high‐power output as well as long cycle life of capacitors in one device. The key point of constructing a high‐performance SIHC is to couple appropriate anode and cathode materials, which can well match in capacity and kinetics behavior simultaneously. In this work, a novel SIHC, coupling a titanium dioxide/carbon nanocomposite (TiO₂/C) anode with a 3D nanoporous carbon cathode, which are both prepared from metal–organic frameworks (MOFs, MIL‐125 (Ti) and ZIF‐8, respectively), is designed and fabricated. The robust architecture and extrinsic pseudocapacitance of TiO₂/C nanocomposite contribute to the excellent cyclic stability and rate capability in half‐cell. Hierarchical 3D nanoporous carbon displays superior capacity and rate performance. Benefiting from the merits of structures and performances of anode and cathode materials, the as‐built SIHC achieves a high energy density of 142.7 W h kg^?1 and a high power output of 25 kW kg^?1 within 1–4 V, as well as an outstanding life span of 10 000 cycles with over 90% of the capacity retention. The results make it competitive in high energy and power–required electricity storage applications.     

Freestanding Metallic 1T MoS2 with Dual Ion Diffusion Paths as High Rate Anode for Sodium‐Ion Batteries

This work studies for the first time the metallic 1T MoS₂ sandwich grown on graphene tube as a freestanding intercalation anode for promising sodium‐ion batteries (SIBs). Sodium is earth‐abundant and readily accessible. Compared to lithium, the main challenge of sodium‐ion batteries is its sluggish ion diffusion kinetic. The freestanding, porous, hollow structure of the electrode allows maximum electrolyte accessibility to benefit the transportation of Na⁺ ions. Meanwhile, the metallic MoS₂ provides excellent electron conductivity. The obtained 1T MoS₂ electrode exhibits excellent electrochemical performance: a high reversible capacity of 313 mAh g^?1 at a current density of 0.05 A g^?1 after 200 cycles and a high rate capability of 175 mAh g^?1 at 2 A g^?1. The underlying mechanism of high rate performance of 1T MoS₂ for SIBs is the high electrical conductivity and excellent ion accessibility. This study sheds light on using the 1T MoS₂ as a novel anode for SIBs.     

Hierarchical Porous Te@ZnCo2O4 Nanofibers Derived from Te@Metal‐Organic Frameworks for Superior Lithium Storage Capability

1D hierarchical porous nanocomposites with tailored chemical composition are gaining popularity in lithium‐ion batteries. Here, with core@shell Te@ZIF‐8 (Zn, Co) nanofibers as a starting point, rational designed porous Te@ZnCo₂O₄ nanocomposite has been fabricated by a simple morphology‐maintained and calcination‐induced oxidative decomposition process, with the purpose of simultaneously settling the pulverization and conductivity issues of transition metal oxides. This is the first time to integrate Te and ZnCo₂O₄ into one architecture at nanometer level. The Te@ZnCo₂O₄ nanofibers combine both advantages of Te such as excellent electrical conductivity and ZnCo₂O₄ with high capacity as well as take full use of their synergistic effect. With the favorable 1D porous structure and the unique composition, this novel Te@ZnCo₂O₄ nanofiber manifests strong ability to improve the lithium storage performances with a high specific capacity of 1364 mA h g^?1 in the initial discharge and a reversible capacity of 956 mA h g^?1 after 100 cycles. When increased the current density to 2000 mA g^?1, the capacity still remains as 307 mA h g^?1, demonstrating superior rate capability. Furthermore, this general strategy can be extended to construct other core@shell Te@MOFs composites.     

MoSe2‐Covered N,P‐Doped Carbon Nanosheets as a Long‐Life and High‐Rate Anode Material for Sodium‐Ion Batteries

MoSe₂ grown on N,P‐co‐doped carbon nanosheets is synthesized by a solvothermal reaction followed with a high‐temperature calcination. This composite has an interlayer spacing of MoSe₂ expanded to facilitate sodium‐ion diffusion, MoSe₂ immobilized on carbon nanosheets to improve charge‐transfer kinetics, and N and P incorporated into carbon to enhance its interaction with active species upon cycling. These features greatly improve the electrochemical performance of this composite, as compared to all the controls. It presents a specific capacity of 378 mAh g^?1 after 1000 cycles at 0.5 A g^?1, corresponding to 87% of the capacity at the second cycle. Ex situ Raman spectra and high‐resolution transmission electron microscopy images confirm that it is element Se, rather than MoSe₂, formed after the charging process. The interaction of the active species with modified carbon is simulated using density functional theory to explain this excellent stability. The superior rate capability, where the capacity at 15 A g^?1 equals ≈55% of that at 0.5 A g^?1, could be associated with the significant contribution of pseudocapacitance. By pairing with homemade Na₃V₂(PO₄)₃/C, this composite also exhibits excellent performances in full cells.     

Few‐Layered SnS2 on Few‐Layered Reduced Graphene Oxide as Na‐Ion Battery Anode with Ultralong Cycle Life and Superior Rate Capability

Na‐ion Batteries have been considered as promising alternatives to Li‐ion batteries due to the natural abundance of sodium resources. Searching for high‐performance anode materials currently becomes a hot topic and also a great challenge for developing Na‐ion batteries. In this work, a novel hybrid anode is synthesized consisting of ultrafine, few‐layered SnS₂ anchored on few‐layered reduced graphene oxide (rGO) by a facile solvothermal route. The SnS₂/rGO hybrid exhibits a high capacity, ultralong cycle life, and superior rate capability. The hybrid can deliver a high charge capacity of 649 mAh g^?1 at 100 mA g^?1. At 800 mA g^?1 (1.8 C), it can yield an initial charge capacity of 469 mAh g^?1, which can be maintained at 89% and 61%, respectively, after 400 and 1000 cycles. The hybrid can also sustain a current density up to 12.8 A g^?1 (≈28 C) where the charge process can be completed in only 1.3 min while still delivering a charge capacity of 337 mAh g^?1. The fast and stable Na‐storage ability of SnS₂/rGO makes it a promising anode for Na‐ion batteries.     

Core–Shell Ge@Graphene@TiO2 Nanofibers as a High‐Capacity and Cycle‐Stable Anode for Lithium and Sodium Ion Battery

Germanium is considered as a promising anode material because of its comparable lithium and sodium storage capability, but it usually exhibits poor cycling stability due to the large volume variation during lithium or sodium uptake and release processes. In this paper, germanium@graphene nanofibers are first obtained through electrospinning followed by calcination. Then atomic layer deposition is used to fabricate germanium@graphene@TiO₂ core–shell nanofibers (Ge@G@TiO₂ NFs) as anode materials for lithium and sodium ion batteries (LIBs and SIBs). Graphene and TiO₂ can double protect the germanium nanofibers in charge and discharge processes. The Ge@G@TiO₂ NFs composite as an anode material is versatile and exhibits enhanced electrochemical performance for LIBs and SIBs. The capacity of the Ge@G@TiO₂ NFs composite can be maintained at 1050 mA h g^?1 (100th cycle) and 182 mA h g^?1 (250th cycle) for LIBs and SIBs, respectively, at a current density of 100 mA g^?1, showing high capacity and good cycling stability (much better than that of Ge nanofibers or Ge@G nanofibers).     

Metal‐Ion (Fe,V, Co,and Ni)‐Doped MnO2 Ultrathin Nanosheets Supported on Carbon Fiber Paper for the Oxygen Evolution Reaction

Manganese dioxides (MnO₂) are considered one of the most attractive materials as an oxygen evolution reaction (OER) electrode due to its low cost, natural abundance, easy synthesis, and environmental friendliness. Here, metal‐ion (Fe, V, Co, and Ni)‐doped MnO₂ ultrathin nanosheets electrodeposited on carbon fiber paper (CFP) are fabricated using a facile anodic co‐electrodeposition method. A high density of nanoclusters is observed on the surface of the carbon fibers consisting of doped MnO₂ ultrathin nanosheets with an approximate thickness of 5 nm. It is confirmed that the metal ions (Fe, V, Co, and Ni) are doped into MnO₂, improving the conductivity of MnO₂. The doped MnO₂ ultrathin nanosheet/CFP and the IrO₂/CFP composite electrodes for OER achieve a low overpotential of 390 and 245 mV to reach 10 mA cm^?2 in 1 m KOH, respectively. The potential of the doped composite electrode for long‐term OER at a constant current density of 20 mA cm^?2 is much lower than that of the pure MnO₂ composite electrode.     

A Polymetallic Metal‐Organic Framework‐Derived Strategy toward Synergistically Multidoped Metal Oxide Electrodes with Ultralong Cycle Life and High Volumetric Capacity

Metal‐organic frameworks (MOFs) are very convenient self‐templated precursors toward functional materials with tunable functionalities. Although a huge family of MOFs has been discovered, conventional MOF‐derived strategies are largely limited to the sole MOF source based on a handful of the metal elements. The limitation in structure and functionalities greatly restrains the maximum performance of MOF‐based materials for fulfilling the practical potential. This study reports a polymetallic MOF‐derived strategy for easy synthesis of metal‐oxide‐based nanohybrids with precisely tailored multicomponent active dopants. A variety of MoO₂‐based nanohybrids with synergistical co‐doping of W, Cu, and P are yielded by controlled pyrolysis of tailor‐made polymetallic MOFs. The W doping induces the formation of Mo_x W_1?x O₂ solid solution with better activity. The homogeneous dispersion of Cu nanocrystallites in robust P‐doped carbon skeleton creates a conductive network for fast charge transfer. Boosting by synergistically multidoping effect, the Mo_0.8W_0.2O₂‐Cu@P‐doped carbon nanohybrids with optimized composition exhibit exceptionally long cycle life of 2000 cycles with high capacities but very slow capacity loss (0.043% per cycle), as well as high power output for lithium storage. Remarkably, the co‐doping of heavy W and Cu elements in MoO₂ with high density makes them particularly suitable for high volumetric lithium storage.     

Shape‐Assisted 2D MOF/Graphene Derived Hybrids as Exceptional Lithium‐Ion Battery Electrodes

Herein, a novel polymer‐templated strategy is described to obtain 2D nickel‐based MOF nanosheets using Ni(OH)₂, squaric acid, and polyvinylpyrrolidone (PVP), where PVP has a dual role as a structure‐directing agent, as well as preventing agglomeration of the MOF nanosheets. Furthermore, a scalable method is developed to transform the 2D MOF sheets to Ni₇S₆/graphene nanosheet (GNS) heterobilayers by in situ sulfidation using thiourea as a sulfur source. The Ni₇S₆/GNS composite shows an excellent reversible capacity of 1010 mAh g^?1 at 0.12 A g^?1 with a Coulombic efficiency of 98% capacity retention. The electrochemical performance of the Ni₇S₆/GNS composite is superior not only to nickel sulfide/graphene‐based composites but also to other metal disulfide–based composite electrodes. Moreover, the Ni₇S₆/GNS anode exhibits excellent cycle stability (≈95% capacity retention after 2000 cycles). This outstanding electrochemical performance can be attributed to the synergistic effects of Ni₇S₆ and GNS, where GNS serves as a conducting matrix to support Ni₇S₆ nanosheets while Ni₇S₆ prevents restacking of GNS. This work opens up new opportunities in the design of novel functional heterostructures by hybridizing 2D MOF nanosheets with other 2D nanomaterials for electrochemical energy storage/conversion applications.     

Controlled Design of Well‐Dispersed Ultrathin MoS2 Nanosheets inside Hollow Carbon Skeleton: Toward Fast Potassium Storage by Constructing Spacious “Houses” for K Ions

The large volume expansion induced by K⁺ intercalation is always a big challenge for designing high‐performance electrode materials in potassium‐ion storage system. Based on the idea that large‐sized ions should accommodate big “houses,” a facile‐induced growth strategy is proposed to achieve the self‐loading of MoS₂ clusters inside a hollow tubular carbon skeleton (HTCS). Meantime, a step‐by‐step intercalation technology is employed to tune the interlayer distance and the layer number of MoS₂. Based on the above, the ED‐MoS₂@CT hybrids are achieved by self‐loading and anchoring the well‐dispersed ultrathin MoS₂ nanosheets on the inner surface of HTCSs. This unique compositing model not only alleviates the mechanical strain efficiently, but also provides spacious “roads” (hollow tubular carbon skeleton) and “houses” (interlayer expanded ultrathin MoS₂ sheets) for fast K⁺ transition and storage. As an anode of potassium‐ion batteries, the resultant ED‐MoS₂@CT electrode delivers a high specific capacity of 148.5 mAh g^?1 at 2 A g^?1 after 10 000 cycles with only 0.002% fading per cycle. The assembled ED‐MoS₂@CT//PC potassium‐ion hybrid supercapacitor device shows a high energy density of 148 Wh kg^?1 at a power density of 965 W kg^?1, which is comparable to that of lithium‐ion hybrid supercapacitors.     

Hard–Soft Composite Carbon as a Long‐Cycling and High‐Rate Anode for Potassium‐Ion Batteries

There exist tremendous needs for sustainable storage solutions for intermittent renewable energy sources, such as solar and wind energy. Thus, systems based on Earth‐abundant elements deserve much attention. Potassium‐ion batteries represent a promising candidate because of the abundance of potassium resources. As for the choices of anodes, graphite exhibits encouraging potassium‐ion storage properties; however, it suffers limited rate capability and poor cycling stability. Here, nongraphitic carbons as K‐ion anodes with sodium carboxymethyl cellulose as the binder are systematically investigated. Compared to hard carbon and soft carbon, a hard–soft composite carbon with 20 wt% soft carbon distributed in the matrix phase of hard carbon microspheres exhibits highly amenable performance: high capacity, high rate capability, and very stable long‐term cycling. In contrast, pure hard carbon suffers limited rate capability, while the capacity of pure soft carbon fades more rapidly.     

Sodium Storage and Electrode Dynamics of Tin–Carbon Composite Electrodes from Bulk Precursors for Sodium‐Ion Batteries

Here, a Sn–C composite material prepared from bulk precursors (tin metal, graphite, and melamine) using ball milling and annealing is reported. The composite (58 wt% Sn and 42 wt% N‐doped carbon) shows a capacity up to 445 mAh g_Sn+C^?1 and an excellent cycle life (1000 cycles). For the graphite, the ball milling leads to graphene nanoplatelets (GnP) for which the storage mechanism changes from solvent co‐intercalation to conventional intercalation. The final composite (Sn at nitrogen‐doped graphite nanoplatelets (SnNGnP)) is obtained by combining the GnPs with Sn and melamine as the nitrogen source. Rate‐dependent measurements and in situ X‐ray diffraction are used to study the asymmetric storage behavior of Sn, which shows a more sloping potential profile during sodiation and more defined steps during desodiation. The disappearance of two redox plateaus during desodiation is linked to the preceding sodiation current density (memory effect). The asymmetric behavior is also found by in situ electrochemical dilatometry. This method also shows that the effective electrode expansion during sodiation is much smaller (about +14%) compared to what is expected from Sn (+420%), which gives a reasonable explanation for the excellent cycle life for the SnNGnP (and likely other nanocomposites in general). Next to the advantages, challenges, which result from the nanocomposite approach, are also discussed.     

Prussian Blue@C Composite as an Ultrahigh‐Rate and Long‐Life Sodium‐Ion Battery Cathode

Rechargeable sodium ion batteries (SIBs) are surfacing as promising candidates for applications in large‐scale energy‐storage systems. Prussian blue (PB) and its analogues (PBAs) have been considered as potential cathodes because of their rigid open framework and low‐cost synthesis. Nevertheless, PBAs suffer from inferior rate capability and poor cycling stability resulting from the low electronic conductivity and deficiencies in the PBAs framework. Herein, to understand the vacancy‐impacted sodium storage and Na‐insertion reaction kinetics, we report on an in‐situ synthesized PB@C composite as a high‐performance SIB cathode. Perfectly shaped, nanosized PB cubes were grown directly on carbon chains, assuring fast charge transfer and Na‐ion diffusion. The existence of [Fe(CN)₆] vacancies in the PB crystal is found to greatly degrade the electrochemical activity of the Fe^LS(C) redox couple via first‐principles computation. Superior reaction kinetics are demonstrated for the redox reactions of the Fe^HS(N) couple, which rely on the partial insertion of Na ions to enhance the electron conduction. The synergistic effects of the structure and morphology results in the PB@C composite achieving an unprecedented rate capability and outstanding cycling stability (77.5 mAh g^?1 at 90 C, 90 mAh g?¹ after 2000 cycles at 20 C with 90% capacity retention).     

Carbon Nanotubes Rooted in Porous Ternary Metal Sulfide@N/S‐Doped Carbon Dodecahedron: Bimetal‐Organic‐Frameworks Derivation and Electrochemical Application for High‐Capacity and Long‐Life Lithium‐Ion Batteries

Lithium ion battery is the predominant power source for portable electronic devices, electrical vehicles, and back‐up electricity storage units for clean and renewable energies. High‐capacity and long‐life electrode materials are essential for the next‐generation Li‐ion battery with high energy density. Here bimetal‐organic‐frameworks synthesis of Co_0.4Zn_0.19S@N and S codoped carbon dodecahedron is shown with rooted carbon nanotubes (Co‐Zn‐S@N‐S‐C‐CNT) for high‐performance Li‐ion battery application. Benefiting from the synergetic effect of two metal sulfide species for Li‐storage at different voltages, mesoporous dodecahedron structure, N and S codoped carbon overlayer and deep‐rooted CNTs network, the product exhibits a larger‐than‐theoretical reversible Li‐storage capacity of 941 mAh g^?1 after 250 cycles at 100 mA g^?1 and excellent high‐rate capability (734, 591, 505 mAh g^?1 after 500 cycles at large current densities of 1, 2, and 5 A g^?1 , respectively).     

Fast Rate and Long Life Potassium‐Ion Based Dual‐Ion Battery through 3D Porous Organic Negative Electrode

Potassium‐based dual ion batteries (K‐DIBs) with potassium cation (K⁺) intercalation graphitic anodes have been investigated for their potential in large‐scale energy storage applications owing to their merits of low cost and environmental friendly. Nonetheless, graphite anodes are plagued by volume expansion from the large K⁺ ions and the co‐intercalation of solvent molecules during the charging. Accordingly, organic materials stand out for the flexible adjustable structures and abundant active sites, which can accommodate cations by multiple functional groups without structural collapse. However, K‐DIBs based on organic anodes have rarely been investigated. Herein, 3D porous dipotassium terephthalate nanosheets are synthesized via a freeze‐dry method as the K‐DIB anode, which can reversibly store K⁺ ions at a fast rate with a high specific capacity and robust stability due to the sufficient redox active sites and diffusion pathways of K⁺ ions in the 3D porous structure. Consequently, a novel K‐DIB configuration combining this fast kinetics organic anode and environmental friendly expanded graphite (EG) cathode is constructed (pK2TP//EG), which exhibits a high specific capacity (68 mAh g^‐1 at 2 C), good rate performance up to 20 C, and long cycling life with a capacity retention ~100% after 2000 cycles, which is the best performance observed among reported K‐DIBs.