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.     

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.     

Low‐Temperature Synthesis of Honeycomb CuP2@C in Molten ZnCl2 Salt for High‐Performance Lithium Ion Batteries

Phosphorus‐rich metal phosphides have very high lithium storage capacities, but they are difficult to prepare. A low‐temperature phosphorization method based on Mg reducing PCl₃ in ZnCl₂ molten salt at 300 °C is developed to synthesize phosphorus‐rich CuP₂@C from a Cu‐MOF derived Cu@C composite. Abnormal oxidation of Cu by Zn²⁺ in the molten salt is observed, which leads to the porous honeycomb nanostructure and homogeneously distributed ultrafine CuP₂ nanocrystals. The honeycomb CuP₂@C exhibits excellent lithium storage performance with high reversible capacity (1146 mAh g^?1 at 0.2 A g^?1) and superior cycling stability (720 mAh g^?1 after 600 cycles at 1.0 A g^?1), showing the promising application of P‐rich metal phosphides in lithium ion batteries.     

Rechargeable Room‐Temperature Na–CO2 Batteries

Developing rechargeable Na–CO₂ batteries is significant for energy conversion and utilization of CO₂. However, the reported batteries in pure CO₂ atmosphere are non‐rechargeable with limited discharge capacity of 200 mAh g^?1. Herein, we realized the rechargeability of a Na–CO₂ battery, with the proposed and demonstrated reversible reaction of 3 CO₂+4 Na?2 Na₂CO₃+C. The battery consists of a Na anode, an ether‐based electrolyte, and a designed cathode with electrolyte‐treated multi‐wall carbon nanotubes, and shows reversible capacity of 60000 mAh g^?1 at 1 A g^?1 (≈1000 Wh kg^?1) and runs for 200 cycles with controlled capacity of 2000 mAh g^?1 at charge voltage <3.7 V. The porous structure, high electro‐conductivity, and good wettability of electrolyte to cathode lead to reduced electrochemical polarization of the battery and further result in high performance. Our work provides an alternative approach towards clean recycling and utilization of CO₂.     

High‐Performance Sodium‐Ion Batteries and Sodium‐Ion Pseudocapacitors Based on MoS2/Graphene Composites

Sodium‐ion energy storage, including sodium‐ion batteries (NIBs) and electrochemical capacitive storage (NICs), is considered as a promising alternative to lithium‐ion energy storage. It is an intriguing prospect, especially for large‐scale applications, owing to its low cost and abundance. MoS₂ sodiation/desodiation with Na ions is based on the conversion reaction, which is not only able to deliver higher capacity than the intercalation reaction, but can also be applied in capacitive storage owing to its typically sloping charge/discharge curves. Here, NIBs and NICs based on a graphene composite (MoS₂/G) were constructed. The enlarged d‐spacing, a contribution of the graphene matrix, and the unique properties of the MoS₂/G substantially optimize Na storage behavior, by accommodating large volume changes and facilitating fast ion diffusion. MoS₂/G exhibits a stable capacity of approximately 350 mAh g^?1 over 200 cycles at 0.25 C in half cells, and delivers a capacitance of 50 F g^?1 over 2000 cycles at 1.5 C in pseudocapacitors with a wide voltage window of 0.1–2.5 V.     

An O3‐type Oxide with Low Sodium Content as the Phase‐Transition‐Free Anode for Sodium‐Ion Batteries

Layered transition metal oxides Na_xMO₂ (M=transition metal) with P2 or O3 structure have attracted attention in sodium‐ion batteries (NIBs). A universal law is found to distinguish structural competition between P2 and O3 types based on the ratio of interlayer distances of the alkali metal layer d_(O‐Na‐O) and transition‐metal layer d_(O‐M‐O). The ratio of about 1.62 can be used as an indicator. O3‐type Na_0.66Mg_0.34Ti_0.66O₂ oxide is prepared as a stable anode for NIBs, in which the low Na‐content (ca. 0.66) usually undergoes a P2‐type structure with respect to Na_xMO₂. This material delivers an available capacity of about 98 mAh g^?1 within a voltage range of 0.4–2.0 V and exhibits a better cycling stability (ca. 94.2 % of capacity retention after 128 cycles). In situ X‐ray diffraction reveals a single‐phase reaction in the discharge–charge process, which is different from the common phase transitions reported in O3‐type electrodes, ensuring long‐term cycling stability.     

Preparation of Nanocrystalline Silicon from SiCl4 at 200 °C in Molten Salt for High‐Performance Anodes for Lithium Ion Batteries

Crystalline Si nanoparticles are prepared by reduction of SiCl₄ with metallic magnesium in the molten salt of AlCl₃ at 200 °C in an autoclave. AlCl₃ not only acts as molten salt, but also participates in the reaction. The related experiments confirm that metallic Mg reduces AlCl₃ to create nascent Al which could immediately reduce SiCl₄ to Si, and the by‐product MgCl₂ would combine with AlCl₃ forming complex of MgAl₂Cl₈. As anode for rechargeable lithium ion batteries, the as‐prepared Si delivers the reversible capacity of 3083 mAh g^?1 at 1.2 A g^?1 after 50 cycles, and 1180 mAh g^?1 at 3 A g^?1 over 500 cycles.     

Stereoselectively Assembled Metal–Organic Framework (MOF) Host for Catalytic Synthesis of Carbon Hybrids for Alkaline‐Metal‐Ion Batteries

Cost‐effective metal‐based nanostructured hybrids have been widely dedicated to potential energy storage and conversion applications. Herein, we develop a facile methodology for the synthesis of precise carbon‐confined hybrid nanostructures by stereoselective assembly accompanied by catalytic pyrolysis. Polyacrylonitrile fiber films favors not only metal‐polymer coordination, but also oriented assembly to ensure the well‐defined nanostructure of the carbon hybrids. During chemical vapor deposition (CVD), cobalt‐nanoparticle‐catalyzed growth of carbon‐nanotube branches driven by organic molecules (e.g. melamine) delivers hierarchical carbon hybrids. The resulting carbon hybrids exhibit outstanding electrochemical performance for metal‐ion batteries, for example, a high specific capacity of 680 mAh g^?1 after 320 cycles (Li‐storage) and 220 mAh g^?1 after 500 cycles (Na‐storage) without decay.     

Use of Graphite as a Highly Reversible Electrode with Superior Cycle Life for Sodium‐Ion Batteries by Making Use of Co‐Intercalation Phenomena

Although being the standard anode material in lithium‐ion batteries (LIBs), graphite so far is considered to fail application in sodium‐ion batteries (NIBs) because the Na‐C system lacks suitable binary intercalation compounds. Here we show that this limitation can be circumvented by using co‐intercalation phenomena in a diglyme‐based electrolyte. The resulting compound is a stage‐I ternary intercalation compound with an estimated stoichiometry of Na(diglyme)₂C₂₀. Highlights of the electrode reaction are its high energy efficiency, the small irreversible loss during the first cycle, and a superior cycle life with capacities close to 100 mAh g^?1 for 1000 cycles and coulomb efficiencies >99.87 %. A one‐to‐one comparison with the analogue lithium‐based cell shows that the sodium‐based system performs better and also withstands higher currents.     

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 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.     

Nanostructured Carbon/Antimony Composites as Anode Materials for Lithium‐Ion Batteries with Long Life

A series of nanostructured carbon/antimony composites have been successfully synthesized by a simple sol–gel, high‐temperature carbon thermal reduction process. In the carbon/antimony composites, antimony nanoparticles are homogeneously dispersed in the pyrolyzed nanoporous carbon matrix. As an anode material for lithium‐ion batteries, the C/Sb10 composite displays a high initial discharge capacity of 1214.6 mAh g^?1 and a reversible charge capacity of 595.5 mAh g^?1 with a corresponding coulombic efficiency of 49 % in the first cycle. In addition, it exhibits a high reversible discharge capacity of 466.2 mAh g^?1 at a current density of 100 mA g^?1 after 200 cycles and a high rate discharge capacity of 354.4 mAh g^?1 at a current density of 1000 mA g^?1. The excellent cycling stability and rate discharge performance of the C/Sb10 composite could be due to the uniform dispersion of antimony nanoparticles in the porous carbon matrix, which can buffer the volume expansion and maintain the integrity of the electrode during the charge–discharge cycles.     

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.     

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.     

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.     

Multi‐Electron Reactions Enabled by Anion‐Based Redox Chemistry for High‐Energy Multivalent Rechargeable Batteries

The development of multivalent metal (such as Mg and Ca) based battery systems is hindered by lack of suitable cathode chemistry that shows reversible multi‐electron redox reactions. Cationic redox centres in the classical cathodes can only afford stepwise single‐electron transfer, which are not ideal for multivalent‐ion storage. The charge imbalance during multivalent ion insertion might lead to an additional kinetic barrier for ion mobility. Therefore, multivalent battery cathodes only exhibit slope‐like voltage profiles with insertion/extraction redox of less than one electron. Taking VS₄ as a model material, reversible two‐electron redox with cationic–anionic contributions is verified in both rechargeable Mg batteries (RMBs) and rechargeable Ca batteries (RCBs). The corresponding cells exhibit high capacities of >300 mAh g^?1 at a current density of 100 mA g^?1 in both RMBs and RCBs, resulting in a high energy density of >300 Wh kg^?1 for RMBs and >500 Wh kg^?1 for RCBs. Mechanistic studies reveal a unique redox activity mainly at anionic sulfides moieties and fast Mg²⁺ ion diffusion kinetics enabled by the soft structure and flexible electron configuration of VS₄.     

A Promising Carbon/g‐C3N4 Composite Negative Electrode for a Long‐Life Sodium‐Ion Battery

2D graphitic carbon nitride (g‐C₃N₄) nanosheets are a promising negative electrode candidate for sodium‐ion batteries (NIBs) owing to its easy scalability, low cost, chemical stability, and potentially high rate capability. However, intrinsic g‐C₃N₄ exhibits poor electronic conductivity, low reversible Na‐storage capacity, and insufficient cyclability. DFT calculations suggest that this could be due to a large Na⁺ ion diffusion barrier in the innate g‐C₃N₄ nanosheet. A facile one‐pot heating of a mixture of low‐cost urea and asphalt is strategically applied to yield stacked multilayer C/g‐C₃N₄ composites with improved Na‐storage capacity (about 2 times higher than that of g‐C₃N₄, up to 254 mAh g^?1), rate capability, and cyclability. A C/g‐C₃N₄ sodium‐ion full cell (in which sodium rhodizonate dibasic is used as the positive electrode) demonstrates high Coulombic efficiency (ca. 99.8 %) and a negligible capacity fading over 14 000 cycles at 1 A g^?1.     

Synthesis of Mesoporous Wall‐Structured TiO2 on Reduced Graphene Oxide Nanosheets with High Rate Performance for Lithium‐Ion Batteries

Mesoporous wall‐structured TiO₂ on reduced graphene oxide (RGO) nanosheets were successfully fabricated through a simple hydrothermal process without any surfactants and annealed at 400 °C for 2 h under argon. The obtained mesoporous structured TiO₂–RGO composites had a high surface area (99 0307 m² g^?1) and exhibited excellent electrochemical cycling (a reversible capacity of 260 mAh g^?1 at 1.2 C and 180 mAh g^?1 at 5 C after 400 cycles), demonstrating it to be a promising method for the development of high‐performance Li‐ion batteries.     

Slope‐Dominated Carbon Anode with High Specific Capacity and Superior Rate Capability for High Safety Na‐Ion Batteries

The comprehensive performance of carbon anodes for Na‐ion batteries (NIBs) is largely restricted by their inferior rate capability and safety issues. Herein, a slope‐dominated carbon anode is achieved at a low temperature of 800 °C, which delivers a high reversible capacity of 263 mA h g^?1 at 0.15C with an impressive initial Coulombic efficiency (ICE) of 80 %. When paired with the NaNi_1/3Fe_1/3Mn_1/3O₂ cathode, the reversible capacity at 6C is still 75 % of that at 0.15C, and 73 % of the capacity is retained after 1000 cycles at 3C. The enhanced Na storage performance could be attributed to the unique microstructure with randomly oriented short carbon layers and the relatively higher defect concentration. Given its robustness, such a low‐temperature carbonization strategy could also be applicable to other precursors and provide a new opportunity to design slope‐dominated carbon anodes for high safety, low‐cost NIBs with excellent ICE and superior rate capability.     

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.