A Robust Solid Electrolyte Interphase Layer Augments the Ion Storage Capacity of Bimetallic‐Sulfide‐Containing Potassium‐Ion Batteries

Metal–organic framework‐derived NiCo_2.5S₄ microrods wrapped in reduced graphene oxide (NCS@RGO) were synthesized for potassium‐ion storage. Upon coordination with organic potassium salts, NCS@RGO exhibits an ultrahigh initial reversible specific capacity (602 mAh g^?1 at 50 mA g^?1) and ultralong cycle life (a reversible specific capacity of 495 mAh g^?1 at 200 mA g^?1 after 1 900 cycles over 314 days). Furthermore, the battery demonstrates a high initial Coulombic efficiency of 78 %, outperforming most sulfides reported previously. Advanced ex situ characterization techniques, including atomic force microscopy, were used for evaluation and the results indicate that the organic potassium salt‐containing electrolyte helps to form thin and robust solid electrolyte interphase layers, which reduce the formation of byproducts during the potassiation–depotassiation process and enhance the mechanical stability of electrodes. The excellent conductivity of the RGO in the composites, and the robust interface between the electrodes and electrolytes, imbue the electrode with useful properties; including, ultrafast potassium‐ion storage with a reversible specific capacity of 402 mAh g^?1 even at 2 A g^?1.     

Electrochromic Poly(chalcogenoviologen)s as Anode Materials for High‐Performance Organic Radical Lithium‐Ion Batteries

A series of electrochromic electron‐accepting poly(chalcogenoviologen)s with multiple, stable, and reversible redox centers were used as anodic materials in organic radical lithium‐ion batteries (ORLIBs). The introduction of heavy atoms (S, Se, and Te) into the viologen scaffold significantly improved the capacity and cycling stability of the ORLIBs. Notably, the poly(Te‐BnV) anode was able to intercalate 20 Li ions and showed higher conductivity and insolubility in the electrolyte, thus contributing to a reversible capacity of 502 mAh g^?1 at 100 mA g^?1 when the Coulombic efficiency approached 100 %. The charged/discharged state of flexible electrochromic batteries fabricated from these anodic materials could be monitored visually owing to the unique electrochromic and redox properties of the materials. This study opens a promising avenue for the development of organic polymer‐based electrodes for flexible hybrid visual electronics.     

A Metal–Organic Compound as Cathode Material with Superhigh Capacity Achieved by Reversible Cationic and Anionic Redox Chemistry for High‐Energy Sodium‐Ion Batteries

Although sodium‐ion batteries (SIBs) are considered as alternatives to lithium‐ion batteries (LIBs), the electrochemical performances, in particular the energy density, are much lower than LIBs. A metal–organic compound, cuprous 7,7,8,8‐tetracyanoquinodimethane (CuTCNQ), is presented as a new kind of cathode material for SIBs. It consists of both cationic (Cu^II↔Cu^I) and anionic (TCNQ⁰↔TCNQ⁻↔ TCNQ²⁻) reversible redox reactions, delivering a discharge capacity as high as 255 mAh g⁻¹ at a current density of 20 mA g⁻¹. The synergistic effect of both redox‐active metal cations and organic anions brings an electrochemical transfer of multiple electrons. The transformation of cupric ions to cuprous ions occurs at near 3.80 V vs. Na⁺/Na, while the full reduction of TCNQ⁰ to TCNQ⁻ happens at 3.00–3.30 V. The remarkably high voltage is attributed to the strong inductive effect of the four cyano groups.     

Fiber‐in‐Tube Design of Co9S8‐Carbon/Co9S8: Enabling Efficient Sodium Storage

The sodium‐ion battery is a promising battery technology owing to its low price and high abundance of sodium. However, the sluggish kinetics of sodium ion makes it hard to achieve high‐rate performance, therefore impairing the power density. In this work, a fiber‐in‐tube Co₉S₈‐carbon(C)/Co₉S₈ is designed with fast sodiation kinetics. The experimental and simulation analysis show that the dominating capacitance mechanism for the high Na‐ion storage performance is due to abundant grain boundaries, three exposed layer interfaces, and carbon wiring in the design. As a result, the fiber‐in‐tube hybrid anode shows a high specific capacity of 616 mAh g^?1 after 150 cycles at 0.5 A g^?1. At 1 A g^?1, a capacity of ca. 451 mAh g^?1 can be achieved after 500 cycles. More importantly, a high energy density of 779 Wh kg^?1 and power density of 7793 W kg^?1 can be obtained simultaneously.     

An Insoluble Benzoquinone‐Based Organic Cathode for Use in Rechargeable Lithium‐Ion Batteries

Application of organic electrode materials in rechargeable batteries has attracted great interest because such materials contain abundant carbon, hydrogen, and oxygen elements. However, organic electrodes are highly soluble in organic electrolytes. An organic electrode of 2,3,5,6‐tetraphthalimido‐1,4‐benzoquinone (TPB) is reported in which rigid groups coordinate to a molecular benzoquinone skeleton. The material is insoluble in aprotic electrolyte, and demonstrates a high capacity retention of 91.4 % (204 mA h g⁻¹) over 100 cycles at 0.2 C. The extended π‐conjugation of the material contributes to enhancement of the electrochemical performance (155 mA h g⁻¹ at 10 C). Moreover, density functional theory calculations suggest that favorable synergistic reactions between multiple carbonyl groups and lithium ions can enhance the initial lithium ion intercalation potential. The described approach may provide a novel entry to next‐generation organic electrode materials with relevance to lithium‐ion batteries.     

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.     

Transformation of Rusty Stainless‐Steel Meshes into Stable,Low‐Cost,and Binder‐Free Cathodes for High‐Performance Potassium‐Ion Batteries

To recycle rusty stainless‐steel meshes (RSSM) and meet the urgent requirement of developing high‐performance cathodes for potassium‐ion batteries (KIB), we demonstrate a new strategy to fabricate flexible binder‐free KIB electrodes via transformation of the corrosion layer of RSSM into compact stack‐layers of Prussian blue (PB) nanocubes (PB@SSM). When further coated with reduced graphite oxide (RGO) to enhance electric conductivity and structural stability, the low‐cost, stable, and binder‐free RGO@PB@SSM cathode exhibits excellent electrochemical performances for KIB, including high capacity (96.8 mAh g⁻¹), high discharge voltage (3.3 V), high rate capability (1000 mA g⁻¹; 42 % capacity retention), and outstanding cycle stability (305 cycles; 75.1 % capacity retention).     

An Aligned and Laminated Nanostructured Carbon Hybrid Cathode for High‐Performance Lithium–Sulfur Batteries

An aligned and laminated sulfur‐absorbed mesoporous carbon/carbon nanotube (CNT) hybrid cathode has been developed for lithium–sulfur batteries with high performance. The mesoporous carbon acts as sulfur host and suppresses the diffusion of polysulfide, while the CNT network anchors the sulfur‐absorbed mesoporous carbon particles, providing pathways for rapid electron transport, alleviating polysulfide migration and enabling a high flexibility. The resulting lithium–sulfur battery delivers a high capacity of 1226 mAh g⁻¹ and achieves a capacity retention of 75 % after 100 cycles at 0.1 C. Moreover, a high capacity of nearly 900 mAh g⁻¹ is obtained for 20 mg cm⁻², which is the highest sulfur load to the best of our knowledge. More importantly, the aligned and laminated hybrid cathode endows the battery with high flexibility and its electrochemical performances are well maintained under bending and after being folded for 500 times.     

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.     

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.     

Antimony/Porous Biomass Carbon Nanocomposites as High‐Capacity Anode Materials for Sodium‐Ion Batteries

Antimony/porous biomass carbon nanocomposites have been prepared by a chemical reduction method and applied as anodes for sodium‐ion batteries. The porous biomass carbon derived from a black fungus had a large Brunauer–Emmett–Teller (BET) surface area of 2233 m² g⁻¹ in which antimony nanoparticles were uniformly distributed in the porous carbon. The as‐prepared antimony/porous biomass carbon nanocomposites exhibited a high reversible sodium storage capacity of 567 mA h g⁻¹ at a current density of 100 mA g⁻¹, extended cycling stability, and good rate capability.     

Ionic Liquid Mediated Synthesis of Lath Shaped CuO Micro‐Assembles as Extremely Stable Anode Material for Lithium‐Ion Batteries

A novel lath‐shaped CuO microassemble consisting of well‐crystalized ultrafine nanocrystals was prepared by an ionothermal method with the assistance of ionic liquids (ILs , 1‐butyl‐3‐methylimidazolium tetrafluoroborate). As anode material of lithium ion batteries, the ILs‐CuO exhibits high specific capacity, durability and good rate performance, superior to bare CuO . At a high current density of 1000 mA •g⁻¹, after 100 cycles, ILs‐CuO still retains a discharge capacity of 483.2 mAh •g⁻¹. The improved electrochemical performances could be ascribed to the unique microscale lath‐shape CuO assembles composed of ultrafine nanostructure.     

Facile Synthesis of Ge@C Core–Shell Nanocomposites for High‐Performance Lithium Storage in Lithium‐Ion Batteries

Herein, we report a facile and “green” synthetic route for the preparation of Ge@C core–shell nanocomposites by using a low‐cost Ge precursor. Field‐emission scanning electron microscopy and transmission electron microscopy analyses confirmed the core–shell nanoarchitecture of the Ge@C nanocomposites, with particle sizes ranging from 60 to 100 nm. Individual Ge nanocrystals were coated by a continuous carbon layer, which had an average thickness of 2 nm. When applied as an anode materials for lithium‐ion batteries, the Ge@C nanocomposites exhibited a high initial discharge capacity of 1670 mAh g^?1 and superior rate capability. In particular, Ge@C nanocomposite electrodes maintained a reversible capacity of 734 mAh g^?1 after repeated cycling at a current density of 800 mA g^?1 over 100 cycles.     

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.     

Dual Dopamine Derived Polydopamine Coated N-Doped Porous Carbon Spheres as a Sulfur Host for High-Performance Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are considered to be one of the most promising energy storage systems owing to their high energy density and low cost. However, their wide application is still limited by the rapid capacity fading. Herein, polydopamine (PDA)-coated N-doped hierarchical porous carbon spheres (NPC@PDA) are reported as sulfur hosts for high-performance Li-S batteries. The NPC core with abundant and interconnected pores provides fast electron/ion transport pathways and strong trapping ability towards lithium polysulfide intermediates. The PDA shell could further suppress the loss of lithium polysulfide intermediates through polar–polar interactions. Benefiting from the dual function design, the NPC/S@PDA composite cathode exhibits an initial capacity of 1331 mAh g⁻¹ and remains at 720 mAh g⁻¹ after 200 cycles at 0.5 C. At the pouch cell level with a high sulfur mass loading, the NPC/S@PDA composite cathode still exhibits a high capacity of 1062 mAh g⁻¹ at a current density of 0.4 mA cm⁻².     

Sulfur‐Rich Phosphorus Sulfide Molecules for Use in Rechargeable Lithium Batteries

A new family of sulfur‐rich phosphorus sulfide molecules (P₄S_10+n ) and their electrochemical reaction mechanism with metallic Li has been explored. These P₄S_10+n molecules are synthesized by the reaction between P₄S₁₀ and S. For Li batteries, the P₄S₄₀ molecule in the series of P₄S_10+n molecules provides the highest capacity, which has a first discharge capacity of 1223 mAh g⁻¹ at 100 mA g⁻¹ and stabilizes at approximately 720 mAh g⁻¹ at 500 mA g⁻¹ after 100 cycles. This new class of sulfur‐rich P₄S_10+n molecules and its electrochemical behavior for room‐temperature Li⁺ storage could provide novel insights for phosphorus sulfide molecules and high‐energy batteries.     

Reversible Redox Chemistry of Azo Compounds for Sodium‐Ion Batteries

Sustainable sodium‐ion batteries (SSIBs) using renewable organic electrodes are promising alternatives to lithium‐ion batteries for the large‐scale renewable energy storage. However, the lack of high‐performance anode material impedes the development of SSIBs. Herein, we report a new type of organic anode material based on azo group for SSIBs. Azobenzene‐4,4′‐dicarboxylic acid sodium salt is used as a model to investigate the electrochemical behaviors and reaction mechanism of azo compound. It exhibits a reversible capacity of 170 mAh g^?1 at 0.2C. When current density is increased to 20C, the reversible capacities of 98 mAh g^?1 can be retained for 2000 cycles, demonstrating excellent cycling stability and high rate capability. The detailed characterizations reveal that azo group acts as an electrochemical active site to reversibly bond with Na⁺. The reversible redox chemistry between azo compound and Na ions offer opportunities for developing long‐cycle‐life and high‐rate SSIBs.     

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.     

Reducing the Charge Carrier Transport Barrier in Functionally Layer‐Graded Electrodes

Lithium‐ion batteries (LIBs) are primary energy storage devices to power consumer electronics and electric vehicles, but their capacity is dramatically decreased at ultrahigh charging/discharging rates. This mainly originates from a high Li‐ion/electron transport barrier within a traditional electrode, resulting in reaction polarization issues. To address this limitation, a functionally layer‐graded electrode was designed and fabricated to decrease the charge carrier transport barrier within the electrode. As a proof‐of‐concept, functionally layer‐graded electrodes composing of TiO₂(B) and reduced graphene oxide (RGO) exhibit a remarkable capacity of 128 mAh g⁻¹ at a high charging/discharging rate of 20 C (6.7 A g⁻¹), which is much higher than that of a traditionally homogeneous electrode (74 mAh g⁻¹) with the same composition. This is evidenced by the improvement of effective Li ion diffusivity as well as electronic conductivity in the functionally layer‐graded electrodes.