Hierarchical Metal Sulfide/Carbon Spheres: A Generalized Synthesis and High Sodium‐Storage Performance

The development of suitable anode materials is far from satisfactory and is a major scientific challenge for a competitive sodium‐ion battery technology. Metal sulfides have demonstrated encouraging results, but still suffer from sluggish kinetics and severe capacity decay associated with the phase change. Herein we show that rational electrode design, that is, building efficient electron/ion mixed‐conducting networks, can overcome the problems resulting from conversion reactions. A general strategy for the preparation of hierarchical carbon‐coated metal sulfide (MS?C) spheres through thermal sulfurization of metal glycerate has been developed. We demonstrate the concept by synthesizing highly uniform hierarchical carbon coated vanadium sulfide (V₂S₃?C) spheres, which exhibit a highly reversibly sodium storage capacity of 777 mAh g^?1 at 100 mA g^?1, excellent rate capability (410 mAh g^?1 at 4000 mA g^?1), and impressive cycling ability.     

General Synthesis of Sulfonate-Based Metal–Organic Framework Derived Composite of MxSy@N/S-Doped Carbon for High-Performance Lithium/Sodium Ion Batteries

A general and simple strategy is realized for the first time for the preparation of metal sulfide (M_xS_y) nanoparticles immobilized into N/S co-doped carbon (NSC) through a one-step pyrolysis method. The organic ligand 1,5-naphthalenedisulfonic acid in the metal–organic framework (MOF) precursor is used as a sulfur source, and metal ions are sulfurized in situ to form M_xS_y nanoparticles, resulting in the formation of M_xS_y/NSC (M=Fe, Co, Cu, Ni, Mn, Zn) composites. Benefiting from the M_xS_y nanoparticles and conductive carbon, a synergistic effect of the composite is achieved. For instance, the composite of Fe₇S₈/NSC as an anode displays excellent long-term cycling stability in lithium/sodium ion batteries. At 5 A g⁻¹, large capacities of 645 mA h g⁻¹ and 426.6 mA h g⁻¹ can be retained after 1500 cycles for the lithium-ion battery and after 1000 cycles for the sodium-ion battery, respectively.     

Transition‐Metal Carbodiimides as Molecular Negative Electrode Materials for Lithium‐ and Sodium‐Ion Batteries with Excellent Cycling Properties

We report evidence for the electrochemical activity of transition‐metal carbodiimides versus lithium and sodium. In particular, iron carbodiimide, FeNCN, can be efficiently used as negative electrode material for alkali‐metal‐ion batteries, similar to its oxide analogue FeO. Based on ⁵⁷Fe Mössbauer and infrared spectroscopy (IR) data, the electrochemical reaction mechanism can be explained by the reversible transformation of the Fe?NCN into Li/Na?NCN bonds during discharge and charge. These new electrode materials exhibit higher capacity compared to well‐established negative electrode references such as graphite or hard carbon. Contrary to its oxide analogue, iron carbodiimide does not require heavy treatments (such as nanoscale tailoring, sophisticated textures, or coating) to obtain long cycle life with current density as high as 9 A g^?1 for hundreds of charge–discharge cycles. Similar to the iron compound, several other transition‐metal carbodiimides M_x(NCN)_y with M=Mn, Cr, Zn can cycle successfully versus lithium and sodium. Their electrochemical activity and performance open the way to the design of a novel family of anode materials.     

Wintersweet‐Flower‐Like CoFe2O4/MWCNTs Hybrid Material for High‐Capacity Reversible Lithium Storage

CoFe₂O₄/multiwalled carbon nanotubes (MWCNTs) hybrid materials were synthesized by a hydrothermal method. Field emission scanning electron microscopy and transmission electron microscopy analysis confirmed the morphology of the as‐prepared hybrid material resembling wintersweet flower “buds on branches”, in which CoFe₂O₄ nanoclusters, consisting of nanocrystals with a size of 5–10 nm, are anchored along carbon nanotubes. When applied as an anode material in lithium ion batteries, the CoFe₂O₄/MWCNTs hybrid material exhibited a high performance for reversible lithium storage. In particular, the hybrid anode material delivered reversible lithium storage capacities of 809, 765, 539, and 359 mA h g^?1 at current densities of 180, 450, 900, and 1800 mA g^?1, respectively. The superior performance of CoFe₂O₄/MWCNTs hybrid materials could be ascribed to the synergistic pinning effect of the wintersweet‐flower‐like nanoarchitecture. This strategy could also be applied to synthesize other metal oxide/CNTs hybrid materials as high‐capacity anode materials for lithium ion batteries.     

Synthesis of Cobalt Sulfide Multi‐shelled Nanoboxes with Precisely Controlled Two to Five Shells for Sodium‐Ion Batteries

We report the synthesis of cobalt sulfide multi‐shelled nanoboxes through metal–organic framework (MOF)‐based complex anion conversion and exchange processes. The polyvanadate ions react with cobalt‐based zeolitic imidazolate framework‐67 (ZIF‐67) nanocubes to form ZIF‐67/cobalt polyvanadate yolk‐shelled particles. The as‐formed yolk‐shelled particles are gradually converted into cobalt divanadate multi‐shelled nanoboxes by solvothermal treatment. The number of shells can be easily controlled from 2 to 5 by varying the temperature. Finally, cobalt sulfide multi‐shelled nanoboxes are produced through ion‐exchange with S^2? ions and subsequent annealing. The as‐obtained cobalt sulfide multi‐shelled nanoboxes exhibit enhanced sodium‐storage properties when evaluated as anodes for sodium‐ion batteries. For example, a high specific capacity of 438 mAh g^?1 can be retained after 100 cycles at the current density of 500 mA g^?1.     

Long‐Life Room‐Temperature Sodium–Sulfur Batteries by Virtue of Transition‐Metal‐Nanocluster–Sulfur Interactions

Room‐temperature sodium–sulfur (RT‐Na/S) batteries hold significant promise for large‐scale application because of low cost of both sodium and sulfur. However, the dissolution of polysulfides into the electrolyte limits practical application. Now, the design and testing of a new class of sulfur hosts as transition‐metal (Fe, Cu, and Ni) nanoclusters (ca. 1.2 nm) wreathed on hollow carbon nanospheres (S@M‐HC) for RT‐Na/S batteries is reported. A chemical couple between the metal nanoclusters and sulfur is hypothesized to assist in immobilization of sulfur and to enhance conductivity and activity. S@Fe‐HC exhibited an unprecedented reversible capacity of 394 mAh g^?1 despite 1000 cycles at 100 mA g^?1, together with a rate capability of 220 mAh g^?1 at a high current density of 5 A g^?1. DFT calculations underscore that these metal nanoclusters serve as electrocatalysts to rapidly reduce Na₂S₄ into short‐chain sulfides and thereby obviate the shuttle effect.     

Dendrite‐Free Sodium Metal Anodes Enabled by a Sodium Benzenedithiolate‐Rich Protection Layer

Sodium metal is an ideal anode material for metal rechargeable batteries, owing to its high theoretical capacity (1166 mAh g^?1), low cost, and earth‐abundance. However, the dendritic growth upon Na plating, stemming from unstable solid electrolyte interphase (SEI) film, is a major and most notable problem. Here, a sodium benzenedithiolate (PhS₂Na₂)‐rich protection layer is synthesized in situ on sodium by a facile method that effectively prevents dendrite growth in the carbonate electrolyte, leading to stabilized sodium metal electrodeposition for 400 cycles (800 h) of repeated plating/stripping at a current density of 1 mA cm^?2. The organic salt, PhS₂Na₂, is found to be a critical component in the protection layer. This finding opens up a new and promising avenue, based on organic sodium slats, to stabilize sodium metals with a protection layer.     

High Performance Full Sodium‐Ion Cell Based on a Nanostructured Transition Metal Oxide as Negative Electrode

A novel design of a sodium‐ion cell is proposed based on the use of nanocrystalline thin films composed of transition metal oxides. X‐ray diffraction, Raman spectroscopy and electron microscopy were helpful techniques to unveil the microstructural properties of the pristine nanostructured electrodes. Thus, Raman spectroscopy revealed the presence of amorphous NiO, α‐Fe₂O₃ (hematite) and γ‐Fe₂O₃ (maghemite). Also, this technique allowed the calculation of an average particle size of 23.4 Å in the amorphous carbon phase in situ generated on the positive electrode. The full sodium‐ion cell performed with a reversible capacity of 100 mA h g^?1 at C/2 with an output voltage of about 1.8 V, corresponding to a specific energy density of about 180 W h kg^?1. These promising electrochemical performances allow these transition metal thin films obtained by electrochemical deposition to be envisaged as serious competitors for future negative electrodes in sodium‐ion batteries.     

Self‐Assembling Synthesis of Free‐standing Nanoporous Graphene–Transition‐Metal Oxide Flexible Electrodes for High‐Performance Lithium‐Ion Batteries and Supercapacitors

The synthesis of nanoporous graphene by a convenient carbon nanofiber assisted self‐assembly approach is reported. Porous structures with large pore volumes, high surface areas, and well‐controlled pore sizes were achieved by employing spherical silica as hard templates with different diameters. Through a general wet‐immersion method, transition‐metal oxide (Fe₃O₄, Co₃O₄, NiO) nanocrystals can be easily loaded into nanoporous graphene papers to form three‐dimensional flexible nanoarchitectures. When directly applied as electrodes in lithium‐ion batteries and supercapacitors, the materials exhibited superior electrochemical performances, including an ultra‐high specific capacity, an extended long cycle life, and a high rate capability. In particular, nanoporous Fe₃O₄–graphene composites can deliver a reversible specific capacity of 1427.5 mAh g^?1 at a high current density of 1000 mA g^?1 as anode materials in lithium‐ion batteries. Furthermore, nanoporous Co₃O₄–graphene composites achieved a high supercapacitance of 424.2 F g^?1. This work demonstrated that the as‐developed freestanding nanoporous graphene papers could have significant potential for energy storage and conversion applications.     

SnS2 Nanoplatelet@Graphene Nanocomposites as High‐Capacity Anode Materials for Sodium‐Ion Batteries

Na‐ion batteries have been attracting intensive investigations as a possible alternative to Li‐ion batteries. Herein, we report the synthesis of SnS₂ nanoplatelet@graphene nanocomposites by using a morphology‐controlled hydrothermal method. The as‐prepared SnS₂/graphene nanocomposites present a unique two‐dimensional platelet‐on‐sheet nanoarchitecture, which has been identified by scanning and transmission electron microscopy. When applied as the anode material for Na‐ion batteries, the SnS₂/graphene nanosheets achieved a high reversible specific sodium‐ion storage capacity of 725 mA h g^?1, stable cyclability, and an enhanced high‐rate capability. The improved electrochemical performance for reversible sodium‐ion storage could be ascribed to the synergistic effects of the SnS₂ nanoplatelet/graphene nanosheets as an integrated hybrid nanoarchitecture, in which the graphene nanosheets provide electronic conductivity and cushion for the active SnS₂ nanoplatelets during Na‐ion insertion and extraction processes.     

Boron‐Doped,Carbon‐Coated SnO2/Graphene Nanosheets for Enhanced Lithium Storage

Heteroatom doping is an effective method to adjust the electrochemical behavior of carbonaceous materials. In this work, boron‐doped, carbon‐coated SnO₂/graphene hybrids (BCTGs) were fabricated by hydrothermal carbonization of sucrose in the presence of SnO₂/graphene nanosheets and phenylboronic acid or boric acid as dopant source and subsequent thermal treatment. Owing to their unique 2D core–shell architecture and B‐doped carbon shells, BCTGs have enhanced conductivity and extra active sites for lithium storage. With phenylboronic acid as B source, the resulting hybrid shows outstanding electrochemical performance as the anode in lithium‐ion batteries with a highly stable capacity of 1165 mA h g^?1 at 0.1 A g^?1 after 360 cycles and an excellent rate capability of 600 mA h g^?1 at 3.2 A g^?1, and thus outperforms most of the previously reported SnO₂‐based anode materials.     

Bimetal‐organic Framework‐derived Co9S8/ZnS@NC Heterostructures for Superior Lithium‐ion Storage

Heterostructure engineering of electrode materials, which is expected to accelerate the ion/electron transport rates driven by a built‐in internal electric field at the heterointerface, offers unprecedented promise in improving their cycling stability and rate performance. Herein, carbon nanotubes with Co₉S₈/ZnS heterostructures embedded in a N‐doped carbon framework (Co₉S₈/ZnS@NC) have been rationally designed via an in‐situ vapor chemical transformation strategy with the aid of thiophene, which not only acted as carbon source for the growth of carbon nanotubes but also as sulfur source for the sulfurization of metal Zn and Co. Density functional theory (DFT) calculation shows an about 3.24 eV electrostatic potential difference between ZnS and Co₉S₈, which results in a strong electrostatic field across the interface that makes electrons transfer from Co₉S₈ to the ZnS side. As expected, a stable cycling performance with reversible capacity of 411.2 mAh g^?1 at 1000 mA g^?1 after 300 cycles, excellent rate capability (324 mAh g^?1 at 2000 A g^?1) and a high percentage of pseudocapacitance contribution (87.5% at 2.2 mv/s) for lithium‐ion batteries (LIBs) are achieved. This work provides a possible strategy for designing multicomponent heterostructural materials for application in energy storage and conversion fields.     

Non‐Conjugated Dicarboxylate Anode Materials for Electrochemical Cells

Classical organic anode materials for Na‐ion batteries are mostly based on conjugated carboxylate compounds, which can stabilize added electrons by the double‐bond reformation mechanism. Now, 1,4‐cyclohexanedicarboxylic acid (C₈H₁₂O₄, CHDA) with a non‐conjugated ring (?C₆H₁₀?) connected with carboxylates is shown to undergo electrochemical reactions with two Na ions, delivering a high charge specific capacity of 284 mA h g^?1 (249 mA h g^?1 after 100 cycles), and good rate performance. First‐principles calculations indicate that hydrogen‐transfer‐mediated orbital conversion from antibonding π* to bonding σ stabilize two added electrons, and reactive intermediate with unpaired electron is suppressed by localization of σ‐bonds and steric hindrance. An advantage of CHDA as an anode material is good reversibility and relatively constant voltage. A large variety of organic non‐conjugated compounds are predicted to be promising anode materials for sodium‐ion batteries.     

Nafion/Titanium Dioxide‐Coated Lithium Anode for Stable Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have shown great potential as high energy‐storage devices. However, the stability of the Li metal anode is still a major concern. This is due to the formation of lithium dendrites and severe side reactions with polysulfide intermediates. We herein develop an anode protection method by coating a Nafion/TiO₂ composite layer on the Li anode to solve these problems. In this architecture, Nafion suppresses the growth of Li dendrites, protects the Li anode, and prevents side reactions between polysulfides and the Li anode. Moreover, doped TiO₂ further improves the ionic conductivity and mechanical properties of the Nafion membrane. Li–S batteries with a Nafion/TiO₂‐coated Li anode exhibit better cycling stability (776 mA h g^?1 after 100 cycles at 0.2 C, 1 C=1672 mA g^?1) and higher rate performance (787 mA h g^?1 at 2 C) than those with a pristine Li anode. This work provides an alternative way to construct stable Li anodes for high‐performance Li–S batteries.     

One‐Pot Synthesis of CoSex–rGO Composite Powders by Spray Pyrolysis and Their Application as Anode Material for Sodium‐Ion Batteries

A simple one‐pot synthesis of metal selenide/reduced graphene oxide (rGO) composite powders for application as anode materials in sodium‐ion batteries was developed. The detailed mechanism of formation of the CoSe_x–rGO composite powders that were selected as the first target material in the spray pyrolysis process was studied. The crumple‐structured CoSe_x–rGO composite powders prepared by spray pyrolysis at 800 °C had a crystal structure consisting mainly of Co_0.85Se with a minor phase of CoSe₂. The bare CoSe_x powders prepared for comparison had a spherical shape and hollow structure. The discharge capacities of the CoSe_x–rGO composite and bare CoSe_x powders in the 50th cycle at a constant current density of 0.3 A g^?1 were 420 and 215 mA h g^?1, respectively, and their capacity retentions measured from the second cycle were 80 and 46 %, respectively. The high structural stability of the CoSe_x–rGO composite powders for repeated sodium‐ion charge and discharge processes resulted in superior sodium‐ion storage properties compared to those of the bare CoSe_x powders.     

A New Anode for Lithium‐Ion Batteries Based on Single‐Walled Carbon Nanotubes and Graphene: Improved Performance through a Binary Network Design

Carbon nanomaterials, especially graphene and carbon nanotubes, are considered to be favorable alternatives to graphite‐based anodes in lithium‐ion batteries, owing to their high specific surface area, electrical conductivity, and excellent mechanical flexibility. However, the limited number of storage sites for lithium ions within the sp²‐carbon hexahedrons leads to the low storage capacity. Thus, rational structure design is essential for the preparation of high‐performance carbon‐based anode materials. Herein, we employed flexible single‐walled carbon nanotubes (SWCNTs) with ultrahigh electrical conductivity as a wrapper for 3D graphene foam (GF) by using a facile dip‐coating process to form a binary network structure. This structure, which offered high electrical conductivity, enlarged the electrode/electrolyte contact area, shortened the electron‐/ion‐transport pathways, and allowed for efficient utilization of the active material, which led to improved electrochemical performance. When used as an anode in lithium‐ion batteries, the SWCNT‐GF electrode delivered a specific capacity of 953 mA h g^?1 at a current density of 0.1 A g^?1 and a high reversible capacity of 606 mA h g^?1 after 1000 cycles, with a capacity retention of 90 % over 1000 cycles at 1 A g^?1 and 189 mA h g^?1 after 2200 cycles at 5 A g^?1.     

Tailored Organic Electrode Material Compatible with Sulfide Electrolyte for Stable All‐Solid‐State Sodium Batteries

All‐solid‐state sodium batteries (ASSSBs) with nonflammable electrolytes and ubiquitous sodium resource are a promising solution to the safety and cost concerns for lithium‐ion batteries. However, the intrinsic mismatch between low anodic decomposition potential of superionic sulfide electrolytes and high operating potentials of sodium‐ion cathodes leads to a volatile cathode–electrolyte interface and undesirable cell performance. Here we report a high‐capacity organic cathode, Na₄C₆O₆, that is chemically and electrochemically compatible with sulfide electrolytes. A bulk‐type ASSSB shows high specific capacity (184 mAh g^?1) and one of the highest specific energies (395 Wh kg^?1) among intercalation compound‐based ASSSBs. The capacity retentions of 76 % after 100 cycles at 0.1 C and 70 % after 400 cycles at 0.2 C represent the record stability for ASSSBs. Additionally, Na₄C₆O₆ functions as a capable anode material, enabling a symmetric all‐organic ASSSB with Na₄C₆O₆ as both cathode and anode materials.     

Sodium‐Ion Storage Properties of FeS–Reduced Graphene Oxide Composite Powder with a Crumpled Structure

The sodium‐ion storage properties of FeS–reduced graphene oxide (rGO) and Fe₃O₄‐rGO composite powders with crumpled structures have been studied. The Fe₃O₄‐rGO composite powder, prepared by one‐pot spray pyrolysis, could be transformed to an FeS‐rGO composite powder through a simple sulfidation treatment. The mean size of the Fe₃O₄ nanocrystals in the Fe₃O₄‐rGO composite powder was 4.4 nm. After sulfidation, FeS nanocrystals of size several hundred nanometers were confined within the crumpled structure of the rGO matrix. The initial discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders were 740 and 442 mA h g^?1, and their initial charge capacities were 530 and 165 mA h g^?1, respectively. The discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders at the 50th cycle were 547 and 150 mA h g^?1, respectively. The FeS‐rGO composite powder showed superior sodium‐ion storage performance compared to the Fe₃O₄‐rGO composite powder.     

Electrochemical Properties and Sodium‐Storage Mechanism of Ag2Mo2O7 as the Anode Material for Sodium‐Ion Batteries

Silver molybdate, Ag₂Mo₂O₇, has been prepared by a conventional solid‐state reaction. Its electrochemical properties as an anode material for sodium‐ion batteries (SIBs) have been comprehensively examined by means of galvanostatic charge–discharge cycling, cyclic voltammetry, and rate performance measurements. At operating voltages between 3.0 and 0.01 V, the electrode delivered a reversible capacity of nearly 190 mA h g^?1 at a current density of 20 mA g^?1 after 70 cycles. Ag₂Mo₂O₇ also demonstrated a good rate capability and long‐term cycle stability, the capacity reaching almost 100 mA h g^?1 at a current density of 500 mA g^?1, with a capacity retention of 55 % over 1000 cycles. Moreover, the sodium storage process of Ag₂Mo₂O₇ has been investigated by means of ex situ XRD, Raman spectroscopy, and HRTEM. Interestingly, the anode decomposes into Ag metal and Na₂MoO₄ during the initial discharge process, and then Na⁺ ions are considered to be inserted into/extracted from the Na₂MoO₄ lattice in the subsequent cycles governed by an intercalation/deintercalation mechanism. Ex situ HRTEM images revealed that Ag metal not only remains unchanged during the sodiation/desodiation processes, but is well dispersed throughout the amorphous matrix, thereby greatly improving the electronic conductivity of the working electrode. The “in situ” decomposition behavior of Ag₂Mo₂O₇ is distinct from that of chemically synthesized, metal‐nanoparticle‐coated electrode materials, and provides strong supplementary insight into the mechanism of such new anode materials for SIBs and may set a precedent for the design of further materials.     

Lithium Germanate (Li2GeO3): A High‐Performance Anode Material for Lithium‐Ion Batteries

A simple, cost‐effective, and easily scalable molten salt method for the preparation of Li₂GeO₃ as a new type of high‐performance anode for lithium‐ion batteries is reported. The Li₂GeO₃ exhibits a unique porous architecture consisting of micrometer‐sized clusters (secondary particles) composed of numerous nanoparticles (primary particles) and can be used directly without further carbon coating which is a common exercise for most electrode materials. The new anode displays superior cycling stability with a retained charge capacity of 725 mAh g^?1 after 300 cycles at 50 mA g^?1. The electrode also offers excellent rate capability with a capacity recovery of 810 mAh g^?1 (94 % retention) after 35 cycles of ascending steps of current in the range of 25–800 mA g^?1 and finally back to 25 mA g^?1. This work emphasizes the importance of exploring new electrode materials without carbon coating as carbon‐coated materials demonstrate several drawbacks in full devices. Therefore, this study provides a method and a new type of anode with high reversibility and long cycle stability.