Hierarchical Interconnected Expanded Graphitic Ribbons Embedded with Amorphous Carbon: An Advanced Carbon Nanostructure for Superior Lithium and Sodium Storage

Carbon materials have attracted considerable attention as anodes for lithium‐ion and sodium‐ion batteries due to their low cost and environmental friendliness. This work reports an advanced carbon nanostructure that takes advantage of the chelation effect of glucose and metal ions, which ensures the uniform dispersion of metal in the precursor. Thus, an effective catalytic conversion from sp³ to sp² carbon occurs, enabling simultaneously formation of pores with catalyzed graphitic structures. Due to the low carbonization temperature and short carbonization time as well as the different catalytic degree of various metals, a series of expanded graphitic layers from 0.34 to 0.44 nm with defects and amorphous carbon structure are obtained. The structure not only offers accessible graphitic spacings for reversible lithium/sodium ion insertion, but also provides abundant active sites for lithium/sodium ion adsorption in the defects and amorphous structure. Moreover, the hierarchical interconnected porous structure combining graphitic ribbons is beneficial for fast electronic/ionic transport and favorable electrolyte permeation. More importantly, such advanced carbon materials prove their feasibility for balancing the pore structure and degree of graphitization. When serving as the electrode material for lithium‐ion and sodium‐ion batteries, excellent electrochemical performance along with fast kinetics and long cycle life is achieved.     

Aerosol‐Assisted Heteroassembly of Oxide Nanocrystals and Carbon Nanotubes into 3D Mesoporous Composites for High‐Rate Electrochemical Energy Storage

Nanostructured composites built from ordinary building units have attracted much attention because of their collective properties for critical applications. Herein, we have demonstrated the heteroassembly of carbon nanotubes and oxide nanocrystals using an aerosol spray method to prepare nanostructured mesoporous composites for electrochemical energy storage. The designed composite architectures show high conductivity and hierarchically structured mesopores, which achieve rapid electron and ion transport in electrodes. Therefore, as‐synthesized carbon nanotube/TiO₂ electrodes exhibit high rate performance through rapid Li⁺ intercalation, making them suitable for ultrafast energy storage devices. Moreover, the synthesis process provides a broadly applicable method to achieve the heteroassembly of vast low‐dimensional building blocks for many important applications.     

3D Heteroatom‐Doped Carbon Nanomaterials as Multifunctional Metal‐Free Catalysts for Integrated Energy Devices

Sustainable and cost‐effective energy generation has become crucial for fulfilling present energy requirements. For this purpose, the development of cheap, scalable, efficient, and reliable catalysts is essential. Carbon‐based heteroatom‐doped, 3D, and mesoporous electrodes are very promising as catalysts for electrochemical energy conversion and storage. Various carbon allotropes doped with a variety of heteroatoms can be utilized for cost‐effective mass production of electrode materials. 3D porous carbon electrodes provide multiple advantages, such as large surface area, maximized exposure to active sites, 3D conductive pathways for efficient electron transport, and porous channels to facilitate electrolyte diffusion. However, it is challenging to synthesize and functionalize isotropic 3D carbon structures. Here, various synthesis processes of 3D porous carbon materials are summarized to understand how their physical and chemical properties together with heteroatom doping dictate the electrochemical catalytic performance. Prospects of attractive 3D carbon structural materials for energy conversion and efficient integrated energy systems are also discussed.     

Layered Transition Metal Dichalcogenide-Based Nanomaterials for Electrochemical Energy Storage

The rapid development of electrochemical energy storage (EES) systems requires novel electrode materials with high performance. A typical 2D nanomaterial, layered transition metal dichalcogenides (TMDs) are regarded as promising materials used for EES systems due to their large specific surface areas and layer structures benefiting fast ion transport. The typical methods for the preparation of TMDs and TMD-based nanohybrids are first summarized. Then, in order to improve the electrochemical performance of various kinds of rechargeable batteries, such as lithium-ion batteries, lithium–sulfur batteries, sodium-ion batteries, and other types of emerging batteries, the strategies for the design and fabrication of layered TMD-based electrode materials are discussed. Furthermore, the applications of layered TMD-based nanomaterials in supercapacitors, especially in untraditional supercapacitors, are presented. Finally, the existing challenges and promising future research directions in this field are proposed.     

3D Graphene Networks Encapsulated with Ultrathin SnS Nanosheets@Hollow Mesoporous Carbon Spheres Nanocomposite with Pseudocapacitance‐Enhanced Lithium and Sodium Storage Kinetics

The lithium and sodium storage performances of SnS anode often undergo rapid capacity decay and poor rate capability owing to its huge volume fluctuation and structural instability upon the repeated charge/discharge processes. Herein, a novel and versatile method is described for in situ synthesis of ultrathin SnS nanosheets inside and outside hollow mesoporous carbon spheres crosslinked reduced graphene oxide networks. Thus, 3D honeycomb‐like network architecture is formed. Systematic electrochemical studies manifest that this nanocomposite as anode material for lithium‐ion batteries delivers a high charge capacity of 1027 mAh g^?1 at 0.2 A g^?1 after 100 cycles. Meanwhile, the as‐developed nanocomposite still retains a charge capacity of 524 mAh g^?1 at 0.1 A g^?1 after 100 cycles for sodium‐ion batteries. In addition, the electrochemical kinetics analysis verifies the basic principles of enhanced rate capacity. The appealing electrochemical performance for both lithium‐ion batteries and sodium‐ion batteries can be mainly related to the porous 3D interconnected architecture, in which the nanoscale SnS nanosheets not only offer decreased ion diffusion pathways and fast Li⁺/Na⁺ transport kinetics, but also the 3D interconnected conductive networks constructed from the hollow mesoporous carbon spheres and reduced graphene oxide enhance the conductivity and ensure the structural integrity.     

生物质玉米秸秆衍生碳材料的制备及其储钠性能

当代农业产生大量农作物秸秆残渣,对环境和生活产生极大影响,尤其是大量的焚烧。因此,农作物残渣的有效利用受到广泛关注。利用玉米秸秆茎髓为碳源,通过简单的高温碳化和化学膨化处理成功地合成了性能优异的碳片。物性结构研究表明,得到的碳材料呈现出天然蜂窝状截面和中空管状阵列结构的纵截面,并具有丰富的孔洞,有利于钠离子传输和扩散。(002)晶面表明,碳片的层间距为0.376nm(石墨为0.335nm),这有利于钠离子的脱嵌,从而提高电池的电化学性能。经1 200℃碳化合成的茎髓碳片(SPCS-1200)比900℃碳化合成的碳材料(SPC-900)表现出更好的储钠性能。在50mA·g-1电流密度下,循环100圈后SPCS-1200可以提供稳定的可逆比容量(203mAh·g-1),而SPC-900的可逆比容量仅为173mAh·g-1。此外,SPCS-1200也显示出优异的倍率性能,在1 000mA·g-1电流密度下比容量为100.7mAh·g-1,在2 000mA·g-1电流密度下表现出65.9mAh·g-1的比容量。然而,在相应的电流密度下,SPC-900分别表现出45.7mAh·g-1和31.2mAh·g-1的比容量。     

Rational Design of MOF-Based Hybrid Nanomaterials for Directly Harvesting Electric Energy from Water Evaporation

The continuous exploration of clean-energy technology is critical for the sustainable development of society. The recent work on the electric energy harvesting from water evaporation has made a significant contribution to the utilization of clean energy for self-powering systems. Here, a novel metal–organic-framework-based hybrid nanomaterial is delicately designed and synthesized by the growth of UIO-66 nanoparticles on 2D AlOOH nanoflakes. Due to the combined merits from the 2D morphology, which is inherited from the AlOOH nanoflakes, and the high surface potential, which originates from the UIO-66 nanoparticles, the device made of the AlOOH/UIO-66 hybrid nanomaterials can harvest electric energy from natural water evaporation. An open-circuit voltage of 1.63 ± 0.10 V can be achieved on the prototype devices made of the hybrid nanomaterial. As a proof-of-concept application, a small electric appliance, e.g., a digital calculator, is powered up by a 3 × 3 device array connected in a combined series–parallel configuration.     

Electrolyte‐Dependent Sodium Ion Transport Behaviors in Hard Carbon Anode

A comprehensive study is conducted on hard carbon (HC) series samples by tuning the graphitic local microstructures systematically as an anode for SIBs in both carbonate‐ (CBE) and glyme‐based electrolytes (GBE). The results reveal more detailed charge storage characters of HCs on the LVP section. 1) The LVP capacity is closely related to the prismatic surface area to the basal plane as well as the bulk density, regardless of electrolyte systems. 2) The glyme‐sodium ion complex can facilitate sodium ion delivery into the internal closed pores of the HCs along with not well‐ordered graphitic structures. 3) The glyme‐mediated sodium ion‐storage behavior causes significant decreases in both surface film resistance and charge transfer resistance, leading to enhanced rate capability. 4) The LVP originates from the formation of pseudo‐metallic sodium nanoclusters, which are the same in a CBE and GBE. These results provide insight into the sodium ion‐storage behaviors of HCs, particularly on the interrelationship between graphitic local microstructures and electrolyte systems. In addition, a high‐performance HC anode with a plateau capacity of ≈300 mA h g^?1 is designed based on the information, and its workability is demonstrated in a full‐cell SIB device.     

Nanostructured Carbon Nitrides for CO2 Capture and Conversion

Carbon nitride (CN), a 2D material composed of only carbon (C) and nitrogen (N), which are linked by strong covalent bonds, has been used as a metal-devoid and visible-light-active photocatalyst owing to its magnificent optoelectronic and physicochemical properties including suitable bandgap, adjustable energy-band positions, tailor-made surface functionalities, low cost, metal-free nature, and high thermal, chemical, and mechanical stabilities. CN-based materials possess a lot of advantages over conventional metal-based inorganic photocatalysts including ease of synthesis and processing, versatile functionalization or doping, flexibility for surface engineering, low cost, sustainability, and recyclability without any leaching of toxic metals from photocorrosion. Carbon nitrides and their hybrid materials have emerged as attractive candidates for CO₂ capture and its reduction into clean and green low-carbon fuels and valuable chemical feedstock by using sustainable and intermittent renewable energy sources of sunlight and electricity through the heterogeneous photo(electro)catalysis. Here, the latest research results in this field are summarized, including implementation of novel functionalized nanostructured CNs and their hybrid heterostructures in meeting the stringent requirements to raise the efficiency of the CO₂ reduction process by using state-of-the-art photocatalysis, electrocatalysis, photoelectrocatalysis, and feedstock reactions. The research in this field is primarily focused on advancement in the synthesis of nanostructured and functionalized CN-based hybrid heterostructured materials. More importantly, the recent past has seen a surge in studies focusing significantly on exploring the mechanism of their application perspectives, which include the behavior of the materials for the absorption of light, charge separation, and pathways for the transport of CO₂ during the reduction process.     

Rational Design of Carbon‐Rich Materials for Energy Storage and Conversion

Carbon‐rich materials have drawn tremendous attention toward a wide spectrum of energy applications due to their superior electronic mobility, good mechanical strength, ultrahigh surface area, and more importantly, abundant diversity in structure and components. Herein, rationally designed and bottom‐up constructed carbon‐rich materials for energy storage and conversion are discussed. The fundamental design principles are itemized for the targeted preparation of carbon‐rich materials and the latest remarkable advances are summarized in terms of emerging dimensions including sp² carbon fragment manipulation, pore structure modulation, topological defect engineering, heteroatom incorporation, and edge chemical regulation. In this respect, the corresponding structure–property relationships of the resultant carbon‐rich materials are comprehensively discussed. Finally, critical perspectives on future challenges of carbon‐rich materials are presented. The progress highlighted here will provide meaningful guidance on the precise design and targeted synthesis of carbon‐rich materials, which are of critical importance for the achievement of performance characteristics highly desirable for urgent energy deployment.     

A Flexible Sulfur‐Enriched Nitrogen Doped Multichannel Hollow Carbon Nanofibers Film for High Performance Sodium Storage

Heteroatom doping is regarded as a promising method to enhance the sodium storage performance of carbon materials. In this work, a sulfur‐enriched N‐doped multichannel hollow carbon nanofiber (denoted as S‐NCNF) film is prepared through electrospinning technology and heat treatment with sublimed sulfur as the flexible anode for sodium ion batteries (NIBs). The S‐NCNF film displays outstanding electrochemical performance, particularly with a high rate capacity (132 mA h g^?1 at the current density of 10 A g^?1) and remarkable long cycling stability (reversible specific capacity of 187 mA h g^?1 at 2 A g^?1 over 2000 cycles). The improved sodium storage performance results from the unique 3D structure, abundant defects, and increased interlayer spacing of S‐NCNFs. The density functional theory calculations demonstrate that nitrogenous carbon nanofibers doping with sulfur could not only promote the adsorption of sodium but also favor electrons' transfer. This strategy has been demonstrated as a general process to design free‐standing carbon‐based thin film with other heteroatom doping.     

Hydrothermally Oxidized Single‐Walled Carbon Nanotube Networks for High Volumetric Electrochemical Energy Storage

Improving volumetric energy density is one of the major challenges in nanostructured carbon electrodes for electrochemical energy storage device applications. Herein, a simple hydrothermal oxidation process of single‐walled carbon nanotube (SWNT) networks in dilute nitric acid is reported, enabling simultaneous physical densification and chemical functionalization of the as‐assembled randomly‐packed SWNT films. After the hydrothermal oxidation process, the density of the SWNT films increases from 0.63 to 1.02 g cm^?3 and a considerable amount of redox‐active oxygen functional groups are introduced on the surface of the SWNTs. The functionalized SWNT films are used as positive electrodes against Li metal negative electrodes for potential Li‐ion capacitors or Li‐ion battery applications. The functionalized SWNT electrodes deliver high volumetric as well as gravimetric capacities, 154 Ah L^?1 and 152 mAh g^?1, respectively, owing to the surface redox reactions between the introduced oxygen functional groups and Li ions. In addition, these electrodes exhibit a remarkable rate‐capability by retaining its high capacity of 94 Ah L^?1 (92 mAh g^?1) at a high discharge rate of 10 A g^?1. These results demonstrate the simple hydrothermal oxidation process as an attractive strategy for improving the volumetric performance of nanostructured carbon electrodes.     

Rational Design and General Synthesis of S‐Doped Hard Carbon with Tunable Doping Sites toward Excellent Na‐Ion Storage Performance

Heteroatom‐doping is a promising strategy to tuning the microstructure of carbon material toward improved electrochemical storage performance. However, it is a big challenge to control the doping sites for heteroatom‐doping and the rational design of doping is urgently needed. Herein, S doping sites and the influence of interlayer spacing for two kinds of hard carbon, perfect structure and vacancy defect structure, are explored by the first‐principles method. S prefers doping in the interlayer for the former with interlayer distance of 3.997 Å, while S is doped on the carbon layer for the latter with interlayer distance of 3.695 Å. More importantly, one step molten salts method is developed as a universal synthetic strategy to fabricate hard carbon with tunable microstructure. It is demonstrated by the experimental results that S‐doping hard carbon with fewer pores exhibits a larger interlayer spacing than that of porous carbon, agreeing well with the theoretical prediction. Furthermore, the S‐doping carbon with larger interlayer distance and fewer pores exhibits remarkably large reversible capacity, excellent rate performance, and long‐term cycling stability for Na‐ion storage. A stable and reversible capacity of ≈200 mAh g^?1 is steadily kept even after 4000 cycles at 1 A g^?1.     

Evolution of 3D Printing Methods and Materials for Electrochemical Energy Storage

Additive manufacturing has revolutionized the building of materials, and 3D-printing has become a useful tool for complex electrode assembly for batteries and supercapacitors. The field initially grew from extrusion-based methods and quickly evolved to photopolymerization printing, while supercapacitor technologies less sensitive to solvents more often involved material jetting processes. The need to develop higher-resolution multimaterial printers is borne out in the performance data of recent 3D printed electrochemical energy storage devices. Underpinning every part of a 3D-printable battery are the printing method and the feed material. These influence material purity, printing fidelity, accuracy, complexity, and the ability to form conductive, ceramic, or solvent-stable materials. The future of 3D-printable batteries and electrochemical energy storage devices is reliant on materials and printing methods that are co-operatively informed by device design. Herein, the material and method requirements in 3D-printable batteries and supercapacitors are addressed and requirements for the future of the field are outlined by linking existing performance limitations to requirements for printable energy-storage materials, casings, and direct printing of electrodes and electrolytes. A guide to materials and printing method choice best suited for alternative-form-factor energy-storage devices to be designed and integrated into the devices they power is thus provided.