Bismuth Nanoparticles Embedded in Carbon Spheres as Anode Materials for Sodium/Lithium‐Ion Batteries

Sodium‐ion batteries (SIBs) are regarded as an attractive alternative to lithium‐ion batteries (LIBs) for large‐scale commercial applications, because of the abundant terrestrial reserves of sodium. Exporting suitable anode materials is the key to the development of SIBs and LIBs. In this contribution, we report on the fabrication of Bi@C microspheres using aerosol spray pyrolysis technique. When used as SIBs anode materials, the Bi@C microsphere delivered a high capacity of 123.5 mAh g^?1 after 100 cycles at 100 mA g^?1. The rate performance is also impressive (specific capacities of 299, 252, 192, 141, and 90 mAh g^?1 are obtained under current densities of 0.1, 0.2, 0.5, 1, and 2 A g^?1, respectively). Furthermore, the Bi@C microsphere also proved to be suitable LIB anode materials. The excellent electrochemical performance for both SIBs and LIBs can attributed to the Bi@C microsphere structure with Bi nanoparticles uniformly dispersed in carbon spheres.     

A Biodegradable Polydopamine‐Derived Electrode Material for High‐Capacity and Long‐Life Lithium‐Ion and Sodium‐Ion Batteries

Polydopamine (PDA), which is biodegradable and is derived from naturally occurring products, can be employed as an electrode material, wherein controllable partial oxidization plays a key role in balancing the proportion of redox‐active carbonyl groups and the structural stability and conductivity. Unexpectedly, the optimized PDA derivative endows lithium‐ion batteries (LIBs) or sodium‐ion batteries (SIBs) with superior electrochemical performances, including high capacities (1818 mAh g^?1 for LIBs and 500 mAh g^?1 for SIBs) and good stable cyclabilities (93 % capacity retention after 580 cycles for LIBs; 100 % capacity retention after 1024 cycles for SIBs), which are much better than those of their counterparts with conventional binders.     

Electrospun Hierarchical CaCo2O4 Nanofibers with Excellent Lithium Storage Properties

Hierarchical CaCo₂O₄ nanofibers (denoted as CCO‐NFs) with a unique hierarchical structure have been prepared by a facile electrospinning method and subsequent calcination in air. The as‐prepared CCO‐NFs are composed of well‐defined ultrathin nanoplates that arrange themselves in an oriented manner to form one‐dimensional (1D) hierarchical structures. The controllable formation process and possible formation mechanism are also discussed. Moreover, as a demonstration of the functional properties of such hierarchical architecture, the 1D hierarchical CCO‐NFs were investigated as materials for lithium‐ion batteries (LIBs) anode; they not only delivers a high reversible capacity of 650 mAh g^?1 at a current of 100 mA g^?1 and with 99.6 % capacity retention over 60 cycles, but they also show excellent rate capability with respect to counterpart nanoplates‐in‐nanofibers and nanoplates. The high specific surface areas as well as the unique feature of hierarchical structures are probably responsible for the enhanced electrochemical performance. Considering their facile preparation and good lithium storage properties, 1D hierarchical CCO‐NFs will hold promise in practical LIBs.     

Pushing Up Lithium Storage through Nanostructured Polyazaacene Analogues as Anode

According to the evidence from both theoretical calculations and experimental findings, conjugated ladder polymers containing large π‐conjugated structure, a high number of nitrogen heteroatoms, and a multiring aromatic system, could be an ideal organic anode candidate for lithium‐ion batteries (LIBs). In this report, we demonstrated that the nanostructured polyazaacene analogue poly(1,6‐dihydropyrazino[2,3g]quinoxaline‐2,3,8‐triyl‐7‐(2H)‐ylidene‐7,8‐dimethylidene) (PQL) shows high performance as anode materials in LIBs: high capacity (1750 mAh g^?1, 0.05C), good rate performance (303 mAh g^?1, 5C), and excellent cycle life (1000 cycles), especially at high temperature of 50 °C. Our results suggest nanostructured conjugated ladder polymers could be alternative electrode materials for the practical application of LIBs.     

Hierarchical Nanotubes Constructed by Co9S8/MoS2 Ultrathin Nanosheets Wrapped with Reduced Graphene Oxide for Advanced Lithium Storage

Nanostructured hybrid metal sulfides have attracted intensive attention due to their fascinating properties that are unattainable by the single‐phased counterpart. Herein, we report an efficient approach to construct cobalt sulfide/molybdenum disulfide (Co₉S₈/MoS₂) wrapped with reduced graphene oxide (rGO). The unique structures constructed by ultrathin nanosheets and synergetic effects benefitting from bimetallic sulfides provide improved lithium ions reaction kinetics, and they retain good structural integrity. Interestingly, the conductive rGO can facilitate electron transfer, increase the electronic conductivity and accommodate the strain during cycling. When evaluated as anode materials for lithium‐ion batteries (LIBs), the resultant reduced graphene oxide‐coated cobalt sulfide/molybdenum disulfide (Co₉S₈/MoS₂@rGO) nanotubes deliver high specific capacities of 1140, 948, 897, 852, 820, 798 and 784 mAh g^?1 at the various discharging current densities of 0.2, 0.5, 1, 2, 3, 4 and 5 A g^?1, respectively. In addition, they can maintain an excellent cycle stability with a discharge capacity of 807 mAh g^?1 at 0.2 A g^?1 after 70 cycles, 787 mAh g^?1 at 1 A g^?1 after 180 cycles and 541 mAh g^?1 at 2 A g^?1 after 200 cycles. The proposed method may offer fundamental understanding for the rational design of other hybrid functional composites with high Li‐storage properties.     

Selective Solid‐Liquid Interface Sulfidation Growth of Hierarchical Copper Sulfide and Its Hybrid Nanoflakes for Superior Lithium‐Ion Storage

Two‐dimensional metal sulfides and their hybrids are emerging as promising candidates in various areas. Yet, it remains challenging to synthesize high‐quality 2D metal sulfides and their hybrids, especially iso‐component hybrids, in a simple and controllable way. In this work, a low‐temperature selective solid‐liquid sulfidation growth method has been developed for the synthesis of CuS nanoflakes and their hybrids. CuS nanoflakes of about 20 nm thickness and co‐component hybrids CuO_x/CuS with variable composition ratios derived from different sulfidation time are obtained after the residual sulfur removal. Besides, benefiting from the mild low‐temperature sulfidation conditions, selective sulfidation is realized between Cu and Fe to yield iso‐component FeO_x/CuS 2D nanoflakes of about 10–20 nm thickness, whose composition ratio is readily tunable by controlling the precursor. The as‐synthesized FeO_x/CuS nanoflakes demonstrate superior lithium storage performance (i. e., 707 mAh g^?1 at 500 mA g^?1 and 627 mAh g^?1 at 1000 mA g^?1 after 450 cycles) when tested as anode materials in LIBs owing to the advantages of the ultrathin 2D nanostructure as well as the lithiation volumetric strain self‐reconstruction effect of the co‐existing two phases during charging/discharging processes.     

Porous ZnO/Co3O4/N‐doped carbon nanocages synthesized via pyrolysis of complex metal–organic framework (MOF) hybrids as an advanced lithium‐ion battery anode

Metal oxides have a large storage capacity when employed as anode materials for lithium‐ion batteries (LIBs). However, they often suffer from poor capacity retention due to their low electrical conductivity and huge volume variation during the charge–discharge process. To overcome these limitations, fabrication of metal oxides/carbon hybrids with hollow structures can be expected to further improve their electrochemical properties. Herein, ZnO‐Co₃O₄ nanocomposites embedded in N‐doped carbon (ZnO‐Co₃O₄@N‐C) nanocages with hollow dodecahedral shapes have been prepared successfully by the simple carbonizing and oxidizing of metal–organic frameworks (MOFs). Benefiting from the advantages of the structural features, i.e. the conductive N‐doped carbon coating, the porous structure of the nanocages and the synergistic effects of different components, the as‐prepared ZnO‐Co₃O₄@N‐C not only avoids particle aggregation and nanostructure cracking but also facilitates the transport of ions and electrons. As a result, the resultant ZnO‐Co₃O₄@N‐C shows a discharge capacity of 2373 mAh g^?1 at the first cycle and exhibits a retention capacity of 1305 mAh g^?1 even after 300 cycles at 0.1 A g^?1. In addition, a reversible capacity of 948 mAh g^?1 is obtained at a current density of 2 A g^?1, which delivers an excellent high‐rate cycle ability.     

Porous Nitrogen‐Doped Carbon Nanotubes Derived from Tubular Polypyrrole for Energy‐Storage Applications

Porous nitrogen‐doped carbon nanotubes (PNCNTs) with a high specific surface area (1765 m² g^?1) and a large pore volume (1.28 cm³ g^?1) have been synthesized from a tubular polypyrrole (T‐PPY). The inner diameter and wall thickness of the PNCNTs are about 55 nm and 22 nm, respectively. This material shows extremely promising properties for both supercapacitors and for encapsulating sulfur as a superior cathode material for high‐performance lithium–sulfur (Li‐S) batteries. At a current density of 0.5 A g^?1, PNCNT presents a high specific capacitance of 210 F g^?1, as well as excellent cycling stability at a current density of 2 A g^?1. When the S/PNCNT composite was tested as the cathode material for Li‐S batteries, the initial discharge capacity was 1341 mAh g^?1 at a current rate of 1 C and, even after 50 cycles at the same rate, the high reversible capacity was retained at 933 mAh g^?1. The promising electrochemical energy‐storage performance of the PNCNTs can be attributed to their excellent conductivity, large surface area, nitrogen doping, and unique pore‐size distribution.     

Construction of CoO/Co‐Cu‐S Hierarchical Tubular Heterostructures for Hybrid Supercapacitors

Hierarchical hollow structures for electrode materials of supercapacitors could enlarge the surface area, accelerate the transport of ions and electrons, and accommodate volume expansion during cycling. Besides, construction of heterostructures would enhance the internal electric fields to regulate the electronic structures. All these features of hierarchical hollow heterostructures are beneficial for promoting the electrochemical properties and stability of electrode materials for high‐performance supercapacitors. Herein, CoO/Co‐Cu‐S hierarchical tubular heterostructures (HTHSs) composed of nanoneedles are prepared by an efficient multi‐step approach. The optimized sample exhibits a high specific capacity of 320 mAh g^?1 (2300 F g^?1) at 2.0 A g^?1 and outstanding cycling stability with 96.5 % of the initial capacity retained after 5000 cycles at 10 A g^?1. Moreover, an all‐solid‐state hybrid supercapacitor (HSC) constructed with the CoO/Co‐Cu‐S and actived carbon shows a stable and high energy density of 90.7 Wh kg^?1 at a power density of 800 W kg^?1.     

A Self‐Standing and Flexible Electrode of Yolk–Shell CoS2 Spheres Encapsulated with Nitrogen‐Doped Graphene for High‐Performance Lithium‐Ion Batteries

Flexible lithium‐ion batteries (LIBs) have recently attracted increasing attention with the fast development of bendable electronic systems. Herein, a facile and template‐free solvothermal method is presented for the fabrication of hybrid yolk–shell CoS₂ and nitrogen‐doped graphene (NG) sheets. The yolk–shell architecture of CoS₂ encapsulated with NG coating is designed for the dual protection of CoS₂ to address the structural and interfacial stability concerns facing the CoS₂ anode. The as‐prepared composite can be assembled into a film, which can be used as a binder‐free and flexible electrode for LIBs that does not require any carbon black conducting additives or current collectors. When evaluating lithium‐storage properties, such a flexible electrode exhibits a high specific capacity of 992 mAh g^?1 in the first reversible discharge capacity at a current rate of 100 mA g^?1 and high reversible capacity of 882 mAh g^?1 after 150 cycles with excellent capacity retention of 89.91 %. Furthermore, a reversible capacity as high as 655 mAh g^?1 is still achieved after 50 cycles even at a high rate of 5 C due to the yolk–shell structure and NG coating, which not only provide short Li‐ion and electron pathways, but also accommodate large volume variation.     

Study of the Lithium Storage Mechanism of N-Doped Carbon-Modified Cu2S Electrodes for Lithium-Ion Batteries

Owing to their high specific capacity and abundant reserve, Cu_xS compounds are promising electrode materials for lithium-ion batteries (LIBs). Carbon compositing could stabilize the Cu_xS structure and repress capacity fading during the electrochemical cycling, but the corresponding Li⁺ storage mechanism and stabilization effect should be further clarified. In this study, nanoscale Cu₂S was synthesized by CuS co-precipitation and thermal reduction with polyelectrolytes. High-temperature synchrotron radiation diffraction was used to monitor the thermal reduction process. During the first cycle, the conversion mechanism upon lithium storage in the Cu₂S/carbon was elucidated by operando synchrotron radiation diffraction and in situ X-ray absorption spectroscopy. The N-doped carbon-composited Cu₂S (Cu₂S/C) exhibits an initial discharge capacity of 425 mAh g⁻¹ at 0.1 A g⁻¹, with a higher, long-term capacity of 523 mAh g⁻¹ at 0.1 A g⁻¹ after 200 cycles; in contrast, the bare CuS electrode exhibits 123 mAh g⁻¹ after 200 cycles. Multiple-scan cyclic voltammetry proves that extra Li⁺ storage can mainly be ascribed to the contribution of the capacitive storage.     

Cost‐Effective Biomass Carbon/Calix[4]Quinone Composites for Lithium Ion Batteries

Searching for new cheap encapsulating materials to decrease the solubility of organic small molecules as the cathode materials in electrolytes and improve the performance of organic lithium‐ion batteries (LIBs) is very important and highly desirable. In this research, we found that a novel cheap biomass carbon (named as PPL), prepared by pyrolyzing calyxes of Physalis Peruviana L, can efficiently encapsulate calix[4]quinone to form composites, which can be used as cathodes in LIBs. The initial discharge capacity of the as‐fabricated battery was 437 mAh g^?1 and could maintain 228 mAh g^?1 after 100 cycles. Even at 1 C, the discharge capacity was still 217 mAh g^?1.     

Multiple Active Sites: Lithium Storage Mechanism of Cu‐TCNQ as an Anode Material for Lithium‐Ion Batteries

Recently, carboxylate metal‐organic framework (MOF) materials were reported to perform well as anode materials for lithium‐ion batteries (LIBs); however, the presumed lithium storage mechanism of MOFs is controversial. To gain insight into the mechanism of MOFs as anode materials for LIBs, a self‐supported Cu‐TCNQ (TCNQ: 7,7,8,8‐tetracyanoquinodimethane) film was fabricated via an in situ redox routine, and directly used as electrode for LIBs. The first discharge and charge specific capacities of the self‐supported Cu‐TCNQ electrode are 373.4 and 219.4 mAh g^?1, respectively. After 500 cycles, the reversible specific capacity of Cu‐TCNQ reaches 280.9 mAh g^?1 at a current density of 100 mA g^?1. Mutually validated data reveal that the high capacity is ascribed to the multiple‐electron redox conversion of both metal ions and ligands, as well as the reversible insertion and desertion of Li⁺ ions into the benzene rings of ligands. This work raises the expectation for MOFs as electrode materials of LIBs by utilizing multiple active sites and provides new clues for designing improved electrode materials for LIBs.     

Compact Coupled Graphene and Porous Polyaryltriazine‐Derived Frameworks as High Performance Cathodes for Lithium‐Ion Batteries

It is highly desirable to develop electroactive organic materials and their derivatives as green alternatives of cathodes for sustainable and cost‐effective lithium‐ion batteries (LIBs) in energy storage fields. Herein, compact two‐dimensional coupled graphene and porous polyaryltriazine‐derived frameworks with tailormade pore structures are fabricated by using various molecular building blocks under ionothermal conditions. The porous nanosheets display nanoscale thickness, high specific surface area, and strong coupling of electroactive polyaryltriazine‐derived frameworks with graphene. All these features make it possible to efficiently depress the dissolution of redox moieties in electrolytes and to boost the electrical conductivity of whole electrode. When employed as a cathode in LIBs, the two‐dimensional porous nanosheets exhibit outstanding cycle stability of 395 mAh g^?1 at 5 A g^?1 for more than 5100 cycles and excellent rate capability of 135 mAh g^?1 at a high current density of 15 A g^?1.     

Tunable and Specific Formation of C@NiCoP Peapods with Enhanced HER Activity and Lithium Storage Performance

The superior properties of nanomaterials with a special structure can provide prospects for highly efficient water splitting and lithium storage. Herein, we fabricated a series of peapodlike C@Ni_2?xCo_xP (x≤1) nanocomposites by an anion‐exchange pathway. The experimental results indicated that the HER activity of C@Ni_2?xCo_xP catalyst is strongly related to the Co/Ni ratio, and the C@NiCoP got the highest HER activity with low onset potential of ～45 mV, small Tafel slope of ～43 mV dec^?1, large exchange current density of 0.21 mA cm^?2, and high long‐term durability (60 h) in 0.5 m H₂SO₄ solutions. Equally importantly, as an anode electrode for lithium batteries, this peapodlike C@NiCoP nanocomposite gives excellent charge–discharge properties (e.g., specific capacity of 670 mAh g^?1 at 0.2 A g^?1 after 350 cycles, and a reversible capacity of 405 mAh g^?1 at a high current rate of 10 A g^?1). The outstanding performance of C@NiCoP in HER and LIBs could be attributed to the synergistic effect of the rational design of peapodlike nanostructures and the introduction of Co element.     

Ascorbic Acid‐Assisted Synthesis of Mesoporous Sodium Vanadium Phosphate Nanoparticles with Highly sp2‐Coordinated Carbon Coatings as Efficient Cathode Materials for Rechargeable Sodium‐Ion Batteries

Herein, mesoporous sodium vanadium phosphate nanoparticles with highly sp²‐coordinated carbon coatings (meso‐Na₃V₂(PO₄)₃/C) were successfully synthesized as efficient cathode material for rechargeable sodium‐ion batteries by using ascorbic acid as both the reductant and carbon source, followed by calcination at 750 °C in an argon atmosphere. Their crystalline structure, morphology, surface area, chemical composition, carbon nature and amount were systematically explored. Following electrochemical measurements, the resultant meso‐Na₃V₂(PO₄)₃/C not only delivered good reversible capacity (98 mAh g^?1 at 0.1 A g^?1) and superior rate capability (63 mAh g^?1 at 1 A g^?1) but also exhibited comparable cycling performance (capacity retention: ≈74 % at 450 cycles at 0.4 A g^?1). Moreover, the symmetrical sodium‐ion full cell with excellent reversibility and cycling stability was also achieved (capacity retention: 92.2 % at 0.1 A g^?1 with 99.5 % coulombic efficiency after 100 cycles). These attributes are ascribed to the distinctive mesostructure for facile sodium‐ion insertion/extraction and their continuous sp²‐coordinated carbon coatings, which facilitate electronic conduction.     

Carbonyl-rich Poly(pyrene-4,5,9,10-tetraone Sulfide) as Anode Materials for High-Performance Li and Na-Ion Batteries

Organic carbonyl electrode materials are widely employed for alkali metal-ion secondary batteries in terms of their sustainability, structure designability and abundant resources. As a typical redox-active organic electrode materials, pyrene-4, 5, 9, 10-tetraone (PT) shows high theoretical capacity due to the rich carbonyl active sites. But its electrochemical behavior in secondary batteries still needs further exploration. Herein, PT-based linear polymers (PPTS) is synthesized with thioether bond as bridging group and then employed as an anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). As expected, PPTS shows improved conductivity and insolubility in the non-aqueous electrolyte. When used as an anode material for LIBs, PPTS delivers a high reversible specific capacity of 697.1 mAh g⁻¹ at 0.1 A g⁻¹ and good rate performance (335.4 mAh g⁻¹ at 1 A g⁻¹). Moreover, a reversible specific capacity of 205.2 mAh g⁻¹ at 0.05 A g⁻¹ could be obtained as an anode material for SIBs.     

General Approach to Single and Hybrid Metal Oxide Fiber Structures for High‐Performance Lithium‐Ion Batteries

Owing to the high specific capacity and energy density, metal oxides have become very promising electrodes for lithium‐ion batteries (LIBs). However, poor electrical conductivity accompanied with inferior cycling stability resulting from large volume changes are the main obstacles to achieve a high reversible capacity and stable cyclability. Herein, a facile and general approach to fabricate SnO₂, Fe₂O₃ and Fe₂O₃/SnO₂ fibers is proposed. The appealing structural features are favorable for offering a shortened lithium‐ion diffusion length, easy access for the electrolyte and reduced volume variation when used as anodes in LIBs. As a consequence, both single and hybrid oxides show satisfactory reversible capacities (1206 mAh g^?1 for Fe₂O₃ and 1481 mAh g^?1 for Fe₂O₃/SnO₂ after 200 cycles at 200 mA g^?1) and long lifespans.     

Freeze‐Drying‐Assisted Synthesis of Hierarchically Porous Carbon/Germanium Hybrid for High‐Efficiency Lithium‐Ion Batteries

Herein, an approach is reported to prepare porous a carbon/Ge (C/Ge) hybrid. In this hybrid, Ge nanoparticles are closely embedded in a highly conductive and flexible carbon matrix. Such a hybrid features a high surface area (128.0 m² g^?1) and a hierarchical micropore–mesopore structure. When used as an anode material in lithium‐ion batteries (LIBs), the as‐prepared hybrid [C/Ge (60.37 %)] exhibits an improved lithium storage performance with regard to its capacity and rate capability compared to its counterparts. More specifically, it can maintain a specific capacity as high as 906 mAh g^?1 at a high current density of 0.6 A g^?1 after 50 cycles. The excellent lithium storage performance of the C/Ge (60.37 %) sample can be attributed to synergetic effects between the carbon matrix and Ge nanoparticles. The method we adopted is simple and effective, and can be extended to fabricate other nanomaterials.     

NiO/CNTs derived from metal-organic frameworks as superior anode material for lithium-ion batteries

In this work, porous NiO microspheres interconnected by carbon nanotubes (NiO/CNTs) were successfully fabricated by the pyrolysis of nickel metal-organic framework precursors with CNTs and evaluated as anode materials for lithium-ion batteries (LIBs). The structures, morphologies, and electrochemical performances of the samples were characterized by X-ray diffraction, N₂ adsorption-desorption, field emission scanning electron microscopy, cyclic voltammetry, galvanostatic charge/discharge tests, and electrochemical impedance spectroscopy, respectively. The results show that the introduction of CNTs can improve the lithium-ion storage performance of NiO/CNT composites. Especially, NiO/CNTs-10 exhibits the highest reversible capacity of 812 mAh g^?1 at 100 mA g^?1 after 100 cycles. Even cycled at 2 A g^?1, it still maintains a stable capacity of 502 mAh g^?1 after 300 cycles. The excellent electrochemical performance of NiO/CNT composites should be attributed to the formation of 3D conductive network structure with porous NiO microspheres linked by CNTs, which benefits the electron transfer ability and the buffering of the volume expansion during the cycling process.