ZIF‐8@ZIF‐67‐Derived Nitrogen‐Doped Porous Carbon Confined CoP Polyhedron Targeting Superior Potassium‐Ion Storage

Potassium ion batteries (KIB) have become a compelling energy‐storage system owing to their cost effectiveness and the high abundance of potassium in comparison with lithium. However, its practical applications have been thwarted by a series of challenges, including marked volume expansion and sluggish reaction kinetics caused by the large radius of potassium ions. In line with this, the exploration of reliable anode materials affording high electrical conductivity, sufficient active sites, and structural robustness is the key. The synthesis of ZIF‐8@ZIF‐67 derived nitrogen‐doped porous carbon confined CoP polyhedron architectures (NC@CoP/NC) to function as innovative KIB anode materials is reported. Such composites enable an outstanding rate performance to harvest a capacity of ≈200 mAh g^?1 at 2000 mA g^?1. Additionally, a high cycling stability can be gained by maintaining a high capacity retention of 93% after 100 cycles at 100 mA g^?1. Furthermore, the potassium ion storage mechanism of the NC@CoP/NC anode is systematically probed through theoretical simulations and experimental characterization. This contribution may offer an innovative and feasible route of emerging anode design toward high performance KIBs.     

Controllable N‐Doped CuCo2O4@C Film as a Self‐Supported Anode for Ultrastable Sodium‐Ion Batteries

Rational synthesis of flexible electrodes is crucial to rapid growth of functional materials for energy‐storage systems. Herein, a controllable fabrication is reported for the self‐supported structure of CuCo₂O₄ nanodots (≈3 nm) delicately inserted into N‐doped carbon nanofibers (named as 3‐CCO@C); this composite is first used as binder‐free anode for sodium‐ion batteries (SIBs). Benefiting from the synergetic effect of ultrasmall CuCo₂O₄ nanoparticles and a tailored N‐doped carbon matrix, the 3‐CCO@C composite exhibits high cycling stability (capacity of 314 mA h g^?1 at 1000 mA g^?1 after 1000 cycles) and high rate capability (296 mA h g^?1, even at 5000 mA g^?1). Significantly, the Na storage mechanism is systematically explored, demonstrating that the irreversible reaction of CuCo₂O₄, which decomposes to Cu and Co, happens in the first discharge process, and then a reversible reaction between metallic Cu/Co and CuO/Co₃O₄ occurrs during the following cycles. This result is conducive to a mechanistic study of highly promising bimetallic‐oxide anodes for rechargeable SIBs.     

Penne‐Like MoS2/Carbon Nanocomposite as Anode for Sodium‐Ion‐Based Dual‐Ion Battery

The dual‐ion battery (DIB) system has attracted great attention owing to its merits of low cost, high energy, and environmental friendliness. However, the DIBs based on sodium‐ion electrolytes are seldom reported due to the lack of appropriate anode materials for reversible Na⁺ insertion/extraction. Herein, a new sodium‐ion based DIB named as MoS₂/C‐G DIB using penne‐like MoS₂/C nanotube as anode and expanded graphite as cathode is constructed and optimized for the first time. The hierarchical MoS₂/C nanotube provides expanded (002) interlayer spacing of 2H‐MoS₂, which facilitates fast Na⁺ insertion/extraction reaction kinetics, thus contributing to improved DIB performance. The MoS₂/C‐G DIB delivers a reversible capacity of 65 mA h g^?1 at 2 C in the voltage window of 1.0–4.0 V, with good cycling performance for 200 cycles and 85% capacity retention, indicating the feasibility of potential applications for sodium‐ion based DIBs.     

Graphitic Carbon Nitride (g‐C3N4)‐Derived N‐Rich Graphene with Tuneable Interlayer Distance as a High‐Rate Anode for Sodium‐Ion Batteries

Heteroatom‐doped carbon materials with expanded interlayer distance have been widely studied as anodes for sodium‐ion batteries (SIBs). However, it remains unexplored to further enlarge the interlayer spacing and reveal the influence of heteroatom doping on carbon nanostructures for developing more efficient SIB anode materials. Here, a series of N‐rich few‐layer graphene (N‐FLG) with tuneable interlayer distance ranging from 0.45 to 0.51 nm is successfully synthesized by annealing graphitic carbon nitride (g‐C₃N₄) under zinc catalysis and selected temperature (T = 700, 800, and 900 °C). More significantly, the correlation between N dopants and interlayer distance of resultant N‐FLG‐T highlights the effect of pyrrolic N on the enlargement of graphene interlayer spacing, due to its stronger electrostatic repulsion. As a consequence, N‐FLG‐800 achieves the optimal properties in terms of interlayer spacing, nitrogen configuration and electronic conductivity. When used as an anode for SIBs, N‐FLG‐800 shows remarkable Na⁺ storage performance with ultrahigh rate capability (56.6 mAh g^?1 at 40 A g^?1) and excellent long‐term stability (211.3 mAh g^?1 at 0.5 A g^?1 after 2000 cycles), demonstrating the effectiveness of material design.     

N‐Doped Carbon Nanofibers with Interweaved Nanochannels for High‐Performance Sodium‐Ion Storage

Although graphite materials have been applied as commercial anodes in lithium‐ion batteries (LIBs), there still remain abundant spaces in the development of carbon‐based anode materials for sodium‐ion batteries (SIBs). Herein, an electrospinning route is reported to fabricate nitrogen‐doped carbon nanofibers with interweaved nanochannels (NCNFs‐IWNC) that contain robust interconnected 1D porous channels, produced by removal of a Te nanowire template that is coelectrospun within carbon nanofibers during the electrospinning process. The NCNFs‐IWNC features favorable properties, including a conductive 1D interconnected porous structure, a large specific surface area, expanded interlayer graphite‐like spacing, enriched N‐doped defects and active sites, toward rapid access and transport of electrolyte and electron/sodium ions. Systematic electrochemical studies indicate that the NCNFs‐IWNC exhibits an impressively high rate capability, delivering a capacity of 148 mA h g^?1 at current density of as high as 10 A g^?1, and has an attractively stable performance over 5000 cycles. The practical application of the as‐designed NCNFs‐IWNC for a full SIBs cell is further verified by coupling the NCNFs‐IWNC anode with a FeFe(CN)₆ cathode, which displays a desirable cycle performance, maintaining acapacity of 97 mA h g^?1 over 100 cycles.     

Mild‐Temperature Solution‐Assisted Encapsulation of Phosphorus into ZIF‐8 Derived Porous Carbon as Lithium‐Ion Battery Anode

The high theoretical capacity of red phosphorus (RP) makes it a promising anode material for lithium‐ion batteries. However, the large volume change of RP during charging/discharging imposes an adverse effect on the cyclability and the rate performance suffers from its low conductivity. Herein, a facile solution‐based strategy is exploited to incorporate phosphorus into the pores of zeolitic imidazole framework (ZIF‐8) derived carbon hosts under a mild temperature. With this method, the blocky RP is etched into the form of polyphosphides anions (PP, mainly P₅^?) so that it can easily diffuse into the pores of porous carbon hosts. Especially, the indelible crystalline surface phosphorus can be effectively avoided, which usually generates in the conventional vapor‐condensation encapsulation method. Moreover, highly‐conductive ZIF‐8 derived carbon hosts with any pore smaller than 3 nm are efficient for loading PP and these pores can alleviate the volume change well. Finally, the composite of phosphorus encapsulated into ZIF‐8 derived porous carbon exhibits a significantly improved electrochemical performance as lithium‐ion battery anode with a high capacity of 786 mAh g^?1 after 100 cycles at 0.1 A g^?1, a good stability within 700 cycles at 1 A g^?1, and an excellent rate performance.     

Superresilient Hard Carbon Nanofabrics for Sodium‐Ion Batteries

Developing supermechanically resilient hard carbon materials that can quickly accommodate sodium ions is highly demanded in fabricating durable anodes for wearable sodium‐ion batteries. Here, an interconnected spiral nanofibrous hard carbon fabric with both remarkable resiliency (e.g., recovery rate as high as 1200 mm s^?1) and high Young's modulus is reported. The hard carbon nanofabrics are prepared by spinning and then carbonizing the reaction product of polyacrylonitrile and polar molecules (melamine). The resulting unique hard carbon possesses a highly disordered carbonaceous structure with enlarged interlayer spacing contributed from the strong electrostatic repulsion of dense pyrrolic nitrogen atoms. Its excellent resiliency remains after intercalation/deintercalation of sodium ions. The outstanding sodium‐storage performance of the derived anode includes excellent gravimetric capacity, high‐power capability, and long‐term cyclic stability. More significantly, with a high loading mass, the hard carbon anode displays a high‐power capacity (1.05 mAh cm^?2 at 2 A g^?1) and excellent cyclic stability. This study provides a unique strategy for the design and fabrication of new hard carbon materials for advanced wearable energy storage systems.     

Size‐Tunable Olive‐Like Anatase TiO2 Coated with Carbon as Superior Anode for Sodium‐Ion Batteries

Olive‐shaped anatase TiO₂ with tunable sizes in nanoscale are designed employing polyvinyl alcohol (PVA) as structure directing agents to exert dramatic impacts on structure shaping and size manipulation. Notably, the introduced PVA simultaneously serves as carbon sources, bringing about a homogenous carbon layer with intimate coupling interfaces for boosted electronic conductivity. Constructed from tiny crystalline grains, the uniformly dispersed carbon‐coated TiO₂ nano‐olives (TOC) possess subtle loose structure internally for prompt Na⁺ transportations. When utilized for sodium‐ion storage, the size effects are increasingly significant at high charge–discharge rates, leading to the much superior rate performances of TOC with the smallest size. Bestowed by the improved Na⁺ adsorption and diffusion kinetics together with the promoted electron transfer, it delivers a high specific capacity of 267 mAh g^?1 at 0.1 C (33.6 mA g^?1) and sustains 110 mAh g^?1 at a rather high rate of 20 C. Even after cycled at 10 C over 1000 cycles, a considerable capacity of 125 mAh g^?1 with a retention of 94.6% is still obtained, highlighting its marvelous long‐term cyclability and high‐rate capabilities.     

Amorphous Red Phosphorus Embedded in Sandwiched Porous Carbon Enabling Superior Sodium Storage Performances

The red P anode for sodium ion batteries has attracted great attention recently due to the high theoretical capacity, but the poor intrinsic electronic conductivity and large volume expansion restrain its widespread applications. Herein, the red P is successfully encapsulated into the cube shaped sandwich‐like interconnected porous carbon building (denoted as P@C‐GO/MOF‐5) via the vaporization–condensation method. Superior cycling stability (high capacity retention of about 93% at 2 A g^?1 after 100 cycles) and excellent rate performance (502 mAh g^?1 at 10 A g^?1) can be obtained for the P@C‐GO/MOF‐5 electrode. The superior electrochemical performance can be ascribed to the successful incorporation of red P into the unique carbon matrix with large surface area and pore volume, interconnected porous structure, excellent electronic conductivity and superior structural stability.     

Designed Formation of Hybrid Nanobox Composed of Carbon Sheathed CoSe2 Anchored on Nitrogen‐Doped Carbon Skeleton as Ultrastable Anode for Sodium‐Ion Batteries

Research on sodium‐ion batteries (SIBs) has recently been revitalized due to the unique features of much lower costs and comparable energy/power density to lithium‐ion batteries (LIBs), which holds great potential for grid‐level energy storage systems. Transition metal dichalcogenides (TMDCs) are considered as promising anode candidates for SIBs with high theoretical capacity, while their intrinsic low electrical conductivity and large volume expansion upon Na⁺ intercalation raise the challenging issues of poor cycle stability and inferior rate performance. Herein, the designed formation of hybrid nanoboxes composed of carbon‐protected CoSe₂ nanoparticles anchored on nitrogen‐doped carbon hollow skeletons (denoted as CoSe₂@C∩NC) via a template‐assisted refluxing process followed by conventional selenization treatment is reported, which exhibits tremendously enhanced electrochemical performance when applied as the anode for SIBs. Specifically, it can deliver a high reversible specific capacity of 324 mAh g^?1 at current density of 0.1 A g^?1 after 200 cycles and exhibit outstanding high rate cycling stability at the rate of 5 A g^?1 over 2000 cycles. This work provides a rational strategy for the design of advanced hybrid nanostructures as anode candidates for SIBs, which could push forward the development of high energy and low cost energy storage devices.     

A Functionalized Carbon Surface for High‐Performance Sodium‐Ion Storage

Sodium‐ion batteries (SIBs) are promising for large‐scale energy storage systems and carbon materials are the most likely candidates for their electrodes. The existence of defects in carbon materials is crucial for increasing the sodium storage ability. However, both the reversible capacity and efficiency need to be further improved. Functionalization is a direct and feasible approach to address this issue. Based on the structural changes in carbon materials produced by surface functionalization, three basic categories are defined: heteroatom doping, grafting of functional groups, and the shielding of defects. Heteroatom doping can improve the electrochemical reactivity, and the grafting of functional groups can promote both the diffusion‐controlled bulk process and surface‐confined capacitive process. The shielding of defects can further increase the efficiency and cyclic stability without sacrificing reversible capacity. In this Review, recent progresses in the ways to produce surface functionalization are presented and the related impact on the physical and chemical properties of carbon materials is discussed. Moreover, the critical issues, challenges, and possibilities for future research are summarized.     

Metal Cation‐Assisted Synthesis of Amorphous B,N Co‐Doped Carbon Nanotubes for Superior Sodium Storage

Nearly inexhaustible sodium sources on earth make sodium ion batteries (SIBs) the best candidate for large‐scale energy storage. However, the main obstacles faced by SIBs are the low rate performance and poor cycle stability caused by the large size of Na⁺ ions. Herein, a universal strategy for synthesizing amorphous metals encapsulated into amorphous B, N co‐doped carbon (a‐M@a‐BCN; M = Co, Ni, Mn) nanotubes by metal cation‐assisted carbonization is explored. The methodology allows tailoring the structures (e.g., length, wall thickness, and metals doping) of a‐M@a‐BCN nannotubes at the molecular level. Furthermore, the amorphous metal sulfide encapsulated into a‐BCN (a‐MS_x@a‐BCN; MS_x: CoS, Ni₃S₂, MnS) nanotubes are obtained by one‐step sulfidation process. The a‐M@a‐BCN and a‐MS_x@a‐BCN possess the larger interlayer spacing (0.40 nm) amorphous carbon nanotube rich in heteroatoms active sites, making them exhibit excellent Na⁺ ions diffusion kinetics and capacitive storage behavior. As SIBs anodes, they show high capacity, excellent rate performance, and long cycle stability.     

Controllable Interlayer Spacing of Sulfur‐Doped Graphitic Carbon Nanosheets for Fast Sodium‐Ion Batteries

The electrochemical behaviors of current graphitic carbons are seriously restricted by its low surface area and insufficient interlayer spacing for sodium‐ion batteries. Here, sulfur‐doped graphitic carbon nanosheets are reported by utilizing sodium dodecyl sulfate as sulfur resource and graphitization additive, showing a controllable interlayer spacing range from 0.38 to 0.41 nm and a high specific surface area up to 898.8 m² g^?1. The obtained carbon exhibits an extraordinary electrochemical activity for sodium‐ion storage with a large reversible capacity of 321.8 mAh g^?1 at 100 mA g^?1, which can be mainly attributed to the expanded interlayer spacing of the carbon materials resulted from the S‐doping. Impressively, superior rate capability of 161.8 mAh g^?1 is reserved at a high current density of 5 A g^?1 within 5000 cycles, which should be ascribed to the fast surface‐induced capacitive behavior derived from its high surface area. Furthermore, the storage processes are also quantitatively evaluated, confirming a mixed storage mechanism of diffusion‐controlled intercalation behavior and surface‐induced capacitive behavior. This study provides a novel route for rationally designing various carbon‐based anodes with enhanced rate capability.