A Pyrazine‐Based Polymer for Fast‐Charge Batteries

The lack of high‐power and stable cathodes prohibits the development of rechargeable metal (Na, Mg, Al) batteries. Herein, poly(hexaazatrinaphthalene) (PHATN), an environmentally benign, abundant and sustainable polymer, is employed as a universal cathode material for these batteries. In Na‐ion batteries (NIBs), PHATN delivers a reversible capacity of 220 mAh g^?1 at 50 mA g^?1, corresponding to the energy density of 440 Wh kg^?1, and still retains 100 mAh g^?1 at 10 Ag^?1 after 50 000 cycles, which is among the best performances in NIBs. Such an exceptional performance is also observed in more challenging Mg and Al batteries. PHATN retains reversible capacities of 110 mAh g^?1 after 200 cycles in Mg batteries and 92 mAh g^?1 after 100 cycles in Al batteries. DFT calculations, X‐ray photoelectron spectroscopy, Raman, and FTIR show that the electron‐deficient pyrazine sites in PHATN are the redox centers to reversibly react with metal ions.     

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.     

Nitrogen‐Doped Hollow Amorphous Carbon Spheres@Graphitic Shells Derived from Pitch: New Structure Leads to Robust Lithium Storage

Nitrogen‐doped mesoporous hollow carbon spheres (NHCS) consisting of hybridized amorphous and graphitic carbon were synthesized by chemical vapor deposition with pitch as raw material. Treatment with HNO₃ vapor was performed to incorporate oxygen‐containing groups on NHCS, and the resulting NHCS‐O showed excellent rate capacity, high reversible capacity, and excellent cycling stability when tested as the anode material in lithium‐ion batteries. The NHCS‐O electrode maintained a reversible specific capacity of 616 mAh g^?1 after 250 cycles at a current rate of 500 mA g^?1, which is an increase of 113 % compared to the pristine hollow carbon spheres. In addition, the NHCS‐O electrode exhibited a reversible capacity of 503 mAh g^?1 at a high current density of 1.5 A g^?1. The superior electrochemical performance of NHCS‐O can be attributed to the hybrid structure, high N and O contents, and rich surface defects.     

One‐Step Pyro‐Synthesis of a Nanostructured Mn3O4/C Electrode with Long Cycle Stability for Rechargeable Lithium‐Ion Batteries

A nanostructured Mn₃O₄/C electrode was prepared by a one‐step polyol‐assisted pyro‐synthesis without any post‐heat treatments. The as‐prepared Mn₃O₄/C revealed nanostructured morphology comprised of secondary aggregates formed from carbon‐coated primary particles of average diameters ranging between 20 and 40 nm, as evidenced from the electron microscopy studies. The N₂ adsorption studies reveal a hierarchical porous feature in the nanostructured electrode. The nanostructured morphology appears to be related to the present rapid combustion strategy. The nanostructured porous Mn₃O₄/C electrode demonstrated impressive electrode properties with reversible capacities of 666 mAh g^?1 at a current density of 33 mA g^?1, good capacity retentions (1141 mAh g^?1 with 100 % Coulombic efficiencies at the 100^th cycle), and rate capabilities (307 and 202 mAh g^?1 at 528 and 1056 mA g^?1, respectively) when tested as an anode for lithium‐ion battery applications.     

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.     

A Bipolar and Self‐Polymerized Phthalocyanine Complex for Fast and Tunable Energy Storage in Dual‐Ion Batteries

Bipolar redox organics have attracted interest as electrode materials for energy storage owing to their flexibility, sustainability and environmental friendliness. However, an understanding of their application in all‐organic batteries, let alone dual‐ion batteries (DIBs), is in its infancy. Herein, we propose a strategy to screen a variety of phthalocyanine‐based bipolar organics. The self‐polymerizable bipolar Cu tetraaminephthalocyanine (CuTAPc) shows multifunctional applications in various energy storage systems, including lithium‐based DIBs using CuTAPc as the cathode material, graphite‐based DIBs using CuTAPc as the anode material and symmetric DIBs using CuTAPc as both the cathode and anode materials. Notably, in lithium‐based DIBs, the use of CuTAPc as the cathode material results in a high discharge capacity of 236 mAh g^?1 at 50 mA g^?1 and a high reversible capacity of 74.3 mAh g^?1 after 4000 cycles at 4 A g^?1. Most importantly, a high energy density of 239 Wh kg^?1 and power density of 11.5 kW kg^?1 can be obtained in all‐organic symmetric DIBs.     

High capacity and cycling stability of poly(diaminoanthraquinone) as an organic cathode for rechargeable lithium batteries

Poly(1,5‐diaminoanthraquinone) is synthesized by oxidative polymerization of diaminoanthraquinone monomers and investigated as an organic host for Li‐storage reaction. Benefiting from its high density of redox‐active, Li⁺‐associable benzoquinone groups attached to conducting polyaniline backbones, this polymer undergoes its cathodic reaction predominately through Li⁺‐insertion/extraction processes, delivering a very high reversible capacity of 285 mAh g^?1. In addition, the PDAQ polymer cathode exhibits an excellent rate capability (125 mAh g^?1 at 800 mA g^?1) and a considerable cyclability with a capacity retention of ～160 mAh g^?1 over 200 cycles, possibly serving as a sustainable, high capacity Li⁺ host cathode for Li‐ion batteries. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 235–238     

Highly Porous NiCoSe4 Microspheres as High‐Performance Anode Materials for Sodium‐Ion Batteries

Binary transition metal selenides have been more promising than single transition metal selenides as anode materials for sodium‐ion batteries (SIBs). However, the controlled synthesis of transition metal selenides, especially those derived from metal‐organic‐frameworks with well‐controlled structure and morphology is still challenging. In this paper, highly porous NiCoSe₄@NC composite microspheres were synthesized by simultaneous carbonization and selenization of a Ni?Co‐based metal‐organic framework (NiCo‐MOF) and characterized by scanning electron microscopy, transition electron microscopy, X‐Ray diffraction, X‐Ray photoelectron spectroscopy and electrochemical techniques. The rationally engineered NiCoSe₄@NC composite exhibits a capacity of 325 mAh g^?1 at a current density of 1 A g^?1, and 277.8 mAh g^?1 at 10 A g^?1. Most importantly, the NiCoSe₄@NC retains a capacity of 293 mAh g^?1 at 1 A g^?1 after 1500 cycles, with a capacity decay rate of 0.025 % per cycle.     

A Dual Plating Battery with the Iodine/[ZnIx(OH2)4−x]2−x Cathode

Plating battery electrodes typically deliver higher specific capacity values than insertion or conversion electrodes because the ion charge carriers represent the sole electrode active mass, and a host electrode is unnecessary. However, reversible plating electrodes are rare for electronically insulating nonmetals. Now, a highly reversible iodine plating cathode is presented that operates on the redox couples of I₂/[ZnI_x(OH₂)_4?x]^2?x in a water‐in‐salt electrolyte. The iodine plating cathode with the theoretical capacity of 211 mAh g^?1 plates on carbon fiber paper as the current collector, delivering a large areal capacity of 4 mAh cm^?2. Tunable femtosecond stimulated Raman spectroscopy coupled with DFT calculations elucidate a series of [ZnI_x(OH₂)_4?x]^2?x superhalide ions serving as iodide vehicles in the electrolyte, which eliminates most free iodide ions, thus preventing the consequent dissolution of the cathode‐plated iodine as triiodides.     

Micro‐MoS2 with Excellent Reversible Sodium‐Ion Storage

Low storage capacity and poor cycling stability are the main drawbacks of the electrode materials for sodium‐ion (Na‐ion) batteries, due to the large radius of the Na ion. Here we show that micro‐structured molybdenum disulfide (MoS₂) can exhibit high storage capacity and excellent cycling and rate performances as an anode material for Na‐ion batteries by controlling its intercalation depth and optimizing the binder. The former method is to preserve the layered structure of MoS₂, whereas the latter maintains the integrity of the electrode during cycling. A reversible capacity of 90 mAh g^?1 is obtained on a potential plateau feature when less than 0.5 Na per formula unit is intercalated into micro‐MoS₂. The fully discharged electrode with sodium alginate (NaAlg) binder delivers a high reversible capacity of 420 mAh g^?1. Both cells show excellent cycling performance. These findings indicate that metal chalcogenides, for example, MoS₂, can be promising Na‐storage materials if their operation potential range and the binder can be appropriately optimized.     

A Black Phosphorus–Graphite Composite Anode for Li‐/Na‐/K‐Ion Batteries

Black phosphorus (BP) is a desirable anode material for alkali metal ion storage owing to its high electronic/ionic conductivity and theoretical capacity. In‐depth understanding of the redox reactions between BP and the alkali metal ions is key to reveal the potential and limitations of BP, and thus to guide the design of BP‐based composites for high‐performance alkali metal ion batteries. Comparative studies of the electrochemical reactions of Li⁺, Na⁺, and K⁺ with BP were performed. Ex situ X‐ray absorption near‐edge spectroscopy combined with theoretical calculation reveal the lowest utilization of BP for K⁺ storage than for Na⁺ and Li⁺, which is ascribed to the highest formation energy and the lowest ion diffusion coefficient of the final potassiation product K₃P, compared with Li₃P and Na₃P. As a result, restricting the formation of K₃P by limiting the discharge voltage achieves a gravimetric capacity of 1300 mAh g^?1 which retains at 600 mAh g^?1 after 50 cycles at 0.25 A g^?1.     

Hydronium‐Ion Batteries with Perylenetetracarboxylic Dianhydride Crystals as an Electrode

We demonstrate for the first time that hydronium ions can be reversibly stored in an electrode of crystalline 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA). PTCDA exhibits a capacity of 85 mAh g⁻¹ at 1 A g⁻¹ after an initial conditioning process. Ex situ X‐ray diffraction revealed reversible and significant structure dilation upon reduction of PTCDA in an acidic electrolyte, which can only be ascribed to hydronium‐ion intercalation. The lattice expansion upon hydronium storage was theoretically explored by first‐principles density functional theory (DFT) calculations, which confirmed the hydronium storage in PTCDA.     

Bio‐Inspired Isoalloxazine Redox Moieties for Rechargeable Aqueous Zinc‐Ion Batteries

Organic electrode materials hold great potential for fabricating sustainable energy storage systems, however, the development of organic redox‐active moieties for rechargeable aqueous zinc‐ion batteries is still at an early stage. Here, we report a bio‐inspired riboflavin‐based aqueous zinc‐ion battery utilizing an isoalloxazine ring as the redox center for the first time. This battery exhibits a high capacity of 145.5 mAh g^?1 at 0.01 A g^?1 and a long‐life stability of 3000 cycles at 5 A g^?1. We demonstrate that isoalloxazine moieties are active centers for reversible zinc‐ion storage by using optical and photoelectron spectroscopies as well as theoretical calculations. Through molecule‐structure tailoring of riboflavin, the obtained alloxazine and lumazine molecules exhibit much higher theoretical capacities of 250.3 and 326.6 mAh g^?1, respectively. Our work offers an effective redox‐active moiety for aqueous zinc batteries and will enrich the valuable material pool for electrode design.     

Biomass‐Derived Porous Carbon with Micropores and Small Mesopores for High‐Performance Lithium–Sulfur Batteries

Biomass‐derived porous carbon BPC‐700, incorporating micropores and small mesopores, was prepared through pyrolysis of banana peel followed by activation with KOH. A high specific BET surface area (2741 m² g^?1), large specific pore volume (1.23 cm³ g^?1), and well‐controlled pore size distribution (0.6–5.0 nm) were obtained and up to 65 wt % sulfur content could be loaded into the pores of the BPC‐700 sample. When the resultant C/S composite, BPC‐700‐S65, was used as the cathode of a Li–S battery, a large initial discharge capacity (ca. 1200 mAh g^?1) was obtained, indicating a good sulfur utilization rate. An excellent discharge capacity (590 mAh g^?1) was also achieved for BPC‐700‐S65 at the high current rate of 4 C (12.72 mA cm^?2), showing its extremely high rate capability. A reversible capacity of about 570 mAh g^?1 was achieved for BPC‐700‐S65 after 500 cycles at 1 C (3.18 mA cm^?2), indicating an outstanding cycling stability.     

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.     

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.     

In‐Situ Fabrication of Bone‐Like CoSe2 Nano‐Thorn Loaded on Porous Carbon Cloth as a Flexible Electrode for Na‐Ion Storage

Sodium‐ion batteries (SIBs) based on flexible electrode materials are being investigated recently for improving sluggish kinetics and developing energy density. Transition metal selenides present excellent conductivity and high capacity; nevertheless, their low conductivity and serious volume expansion raise challenging issues of inferior lifespan and capacity fading. Herein, an in‐situ construction method through carbonization and selenide synergistic effect is skillfully designed to synthesize a flexible electrode of bone‐like CoSe₂ nano‐thorn coated on porous carbon cloth. The designed flexible CoSe₂ electrode with stable structural feature displays enhanced Na‐ion storage capabilities with good rate performance and outstanding cycling stability. As expected, the designed SIBs with flexible BL?CoSe₂/PCC electrode display excellent reversible capacity with 360.7 mAh g^?1 after 180 cycles at a current density of 0.1 A g^?1.     

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.     

MoS2 Nanoflowers with Expanded Interlayers as High‐Performance Anodes for Sodium‐Ion Batteries

MoS₂ nanoflowers with expanded interlayer spacing of the (002) plane were synthesized and used as high‐performance anode in Na‐ion batteries. By controlling the cut‐off voltage to the range of 0.4–3 V, an intercalation mechanism rather than a conversion reaction is taking place. The MoS₂ nanoflower electrode shows high discharge capacities of 350 mAh g^?1 at 0.05 A g^?1, 300 mAh g^?1 at 1 A g^?1, and 195 mAh g^?1 at 10 A g^?1. An initial capacity increase with cycling is caused by peeling off MoS₂ layers, which produces more active sites for Na⁺ storage. The stripping of MoS₂ layers occurring in charge/discharge cycling contributes to the enhanced kinetics and low energy barrier for the intercalation of Na⁺ ions. The electrochemical reaction is mainly controlled by the capacitive process, which facilitates the high‐rate capability. Therefore, MoS₂ nanoflowers with expanded interlayers hold promise for rechargeable Na‐ion batteries.     

Porous Carbon Anodes for a High Capacity Lithium‐Ion Battery Obtained by Incorporating Silica into Benzoxazine During Polymerization

Porous carbon anodes with a controllable V_mes/V_mic ratio were synthesized through the self‐assembly of poly(benzoxazine‐co‐resol) and the simultaneous hydrolysis of tetraethyl orthosilicate (TEOS) followed by carbonization and removal of silica. The V_mes/V_mic ratio of the carbon can be controlled in the range of approximately 1.3–32.6 through tuning the amount of TEOS. For lithium‐ion battery anodes, a correlation between the electrochemical performance and V_mes/V_mic ratio has been established. A high V_mes/V_mic ratio in porous carbons is favorable for enhancing the accessibility of Li ions to active sites provided by the micropores and for achieving good lithium storage performance. The obtained porous carbon exhibits a high reversible capacity of 660 mAh g^?1 after 70 cycles at a current density of 100 mA g^?1. Moreover, at a high current density of 3000 mA g^?1, the capacity still remains at 215 mAh g^?1, showing a fast charge‐discharge potential. This synthesis method relying on modified benzoxazine chemistry with the hydrolysis of TEOS may provide a new route for the development of mesoporous carbon‐based electrode materials.