N‐Doping and Defective Nanographitic Domain Coupled Hard Carbon Nanoshells for High Performance Lithium/Sodium Storage

Hard carbons (HCs) possess high lithium/sodium storage capacities, which however suffer from low electric conductivity and poor ion diffusion kinetics. An efficient structure design with appropriate heteroatoms doping and optimized graphitic/defective degree is highly desired to tackle these problems. This work reports a new design of N‐doped HC nanoshells (N‐GCNs) with homogeneous defective nanographite domains, fabricated through the prechelation between Ni²⁺ and chitosan and subsequent catalyst confined graphitization. The as‐prepared N‐GCNs deliver a high reversible lithium storage capacity of 1253 mA h g^?1, with outstanding rate performance (175 mA h g^?1 at a high rate of 20 A g^?1) and good cycling stability, which outperforms most state‐of‐the‐art HCs. Meanwhile, a high reversible sodium storage capacity of 325 mA h g^?1 is also obtained, which stabilizes at 174 mA h g^?1 after 200 cycles. Density functional theory calculations are performed to uncover the coupling effect between heteroatom‐doping and the defective nanographitic domains down to the atomic scale. The in situ Raman analysis reveals the “adsorption mechanism” for sodium storage and the “adsorption–intercalation mechanism” for lithium storage of N‐GCNs.     

Temperature‐Mediated Engineering of Graphdiyne Framework Enabling High‐Performance Potassium Storage

Graphdiyne (GDY), an emerging type of carbon allotropes, possesses fascinating electrical, chemical, and mechanical properties to readily spark energy applications in the realm of Li‐ion and Na‐ion batteries. Nevertheless, rational design of GDY architectures targeting advanced K‐ion storage has rarely been reported to date. Herein, the first example of synthesizing GDY frameworks in a scalable fashion to realize superb potassium storage for high‐performance K‐ion battery (KIB) anodes is showcased. To begin with, first principles calculations provide theoretical guidances for analyzing the intrinsic potassium storage capability of GDY. Meanwhile, the specific capacity is predicted to be as high as 620 mAh g^?1, which is considerably augmented as compared with graphite (278 mAh g^?1). Experimental tests then reveal that prepared GDY framework indeed harvests excellent electrochemical performance as a KIB anode, achieving high specific capacity (≈505 mAh g^?1 at 50 mA g^?1), outstanding rate performance (150 mAh g^?1 at 5000 mA g^?1) and favorable cycling stability (a high capacity retention of over 90% after 2000 cycles at 1000 mA g^?1). Furthermore, kinetic analysis reveals that capacitive effect mainly accounts for the K‐ion storage, with operando Raman spectroscopy/ex situ X‐ray photoelectron spectroscopy identifying good electrochemical reversibility of GDY.     

Radially Aligned Porous Carbon Nanotube Arrays on Carbon Fibers: A Hierarchical 3D Carbon Nanostructure for High‐Performance Capacitive Energy Storage

A novel and scalable synthesis approach to produce hierarchically aligned porous carbon nanotube arrays (PCNTAs) on flexible carbon fibers (CFs) is developed. The PCNTAs are obtained by catalytic conversion of ethanol on ZnO nanorod arrays and then reduction‐evaporation of ZnO nanorods, resulting in uniform and controllable wall thicknesses of the final PCNTAs. The 3D arrangement, the diameters, and the lengths of the PCNTAs can be tuned by adjusting the synthesis protocols of the ZnO nanorod arrays. The PCNTAs@CFs exhibit a high specific capacitance of 182 F g^?1 at 40 A g^?1 (188 F g^?1 at 20 A g^?1) in 6 m KOH. The symmetric supercapacitor shows an excellent cycling stability with only 0.0016% loss per cycle after 10 000 continuous cycles at the current density of 12 A g^?1. These excellent electrochemical performances are ascribed to the unique structural design of hierarchical PCNTAs, which provide not only appropriate channels for enhanced electronic and ionic transport but also increased surface area for accessing more electrolyte ions. The structural design and the synthesis approach are general and can be extended to synthesizing a broad range of materials systems.     

Toward High‐Performance Capacitive Potassium‐Ion Storage: A Superior Anode Material from Silicon Carbide‐Derived Carbon with a Well‐Developed Pore Structure

Potassium‐ion battery (PIB) using a carbon‐based anode is an ideal device for electrochemical energy storage. However, the large atomic size of potassium ions inevitably leads to huge volume expansion and the collapse of anodes, resulting in the severe capacity fading during the long‐term cycling. Herein, silicon carbide‐derived carbon (SiC‐CDC) with a controllable pore structure is synthesized with a concise etching approach. It exhibits a maximum capacity of 284.8 mA h g^?1 at a current density of 0.1 A g^?1 after 200 cycles as well as a highly reversible capacity of 197.3 mA h g^?1 at a current density of 1.0 A g^?1 even after 1000 cycles. A mixed mechanism of the potassium storage is proposed for this prominent performance. The interconnected pore structure with a high proportion of mesopore volume provides abundant active sites for the adsorption of potassium ions, a shortened electrolyte penetration path, and enlarged accumulation space for potassium ions, eventually leading to facilitated capacitive potassium storage inside this SiC‐CDC electrode. This work provides fundamental theories of designing pore structures for boosting capacitive potassium storage and unveils CDC‐based materials as the prospective anodes for high‐performance PIBs.     

Designing 3D Biomorphic Nitrogen‐Doped MoSe2/Graphene Composites toward High‐Performance Potassium‐Ion Capacitors

Potassium‐ion hybrid capacitors (KICs) reconciling the advantages of batteries and supercapacitors have stimulated growing attention for practical energy storage because of the high abundance and low cost of potassium sources. Nevertheless, daunting challenge remains for developing high‐performance potassium accommodation materials due to the large radius of potassium ions. Molybdenum diselenide (MoSe₂) has recently been recognized as a promising anode material for potassium‐ion batteries, achieving high capacity and favorable cycling stability. However, KICs based on MoSe₂ are scarcely demonstrated by far. Herein, a diatomite‐templated synthetic strategy is devised to fabricate nitrogen‐doped MoSe₂/graphene (N‐MoSe₂/G) composites with favorable pseudocapacitive potassium storage targeting a superior anode material for KICs. Benefiting from the unique biomorphic structure, high electron/K‐ion conductivity, enriched active sites, and the conspicuous pseudocapacitive effect of N‐MoSe₂/G, thus‐derived KIC full‐cell manifests high energy/power densities (maximum 119 Wh kg^?1/7212 W kg^?1), outperforming those of recently reported KIC counterparts. Furthermore, the potassium storage mechanism of N‐MoSe₂/G composite is systematically explored with the aid of first‐principles calculations in combination of in situ X‐ray diffraction and ex situ Raman spectroscopy/transmission electron microscopy/X‐ray photoelectron spectroscopy.     

Fe2O3 Nanoneedles on Ultrafine Nickel Nanotube Arrays as Efficient Anode for High‐Performance Asymmetric Supercapacitors

High performance of electrochemical energy storage devices depends on the smart structure engineering of electrodes, including the tailored nanoarchitectures of current collectors and subtle hybridization of active materials. To improve the anode supercapacitive performance of Fe₂O₃ for high‐voltage asymmetric supercapacitors, here, a hybrid core‐branch nanoarchitecture is proposed by integrating Fe₂O₃ nanoneedles on ultrafine Ni nanotube arrays (NiNTAs@Fe₂O₃ nanoneedles). The fabrication process employs a bottom‐up strategy via a modified template‐assisted method starting from ultrafine ZnO nanorod arrays, ensuring the formation of ultrafine Ni nanotube arrays with ultrathin tube walls. The novel developed NiNTAs@Fe₂O₃ nanoneedle electrode is demonstrated to be a highly capacitive anode (418.7 F g^?1 at 10 mV s^?1), matching well with the similarly built NiNTAs@MnO₂ nanosheet cathode. Contributed by the efficient electron collection paths and short ion diffusion paths in the uniquely designed anode and cathode, the asymmetric supercapacitors exhibit an excellent maximum energy density of 34.1 Wh kg^?1 at the power density of 3197.7 W kg^?1 in aqueous electrolyte and 32.2 Wh kg^?1 at the power density of 3199.5 W kg^?1 in quasi‐solid‐state gel electrolyte.     

Creating Effective Nanoreactors on Carbon Nanotubes with Mechanochemical Treatments for High‐Areal‐Capacity Sulfur Cathodes and Lithium Anodes

Li‐S batteries can potentially deliver high energy density and power, but polysulfide shuttle and lithium dendrite formations on Li metal anode have been the major hurdle. The polysulfide shuttle becomes severe particularly when the areal loading of the active material (sulfur) is increased to deliver the high energy density and the charge/discharge current density is raised to deliver high power. This study reports a novel mechanochemical method to create trenches on the surface of carbon nanotubes (CNTs) in free‐standing 3D porous CNT sponges. Unique spiral trenches are created by pressures during the chemical treatment process, providing polysulfide‐philic surfaces for cathode and lithiophilic surfaces for anode. The Li‐S cells made from manufacturing‐friendly sulfur‐sandwiched cathodes and lithium‐infused anodes using the mechanochemically treated electrodes exhibit a strikingly high areal capacity as high as 13.3 mAh cm^?2, which is only marginally reduced even with a tenfold increase in current density (16 mA cm^?2), demonstrating both high “cell‐level” energy density and power. The outstanding performance can be attributed to the significantly improved reaction kinetics and lowered overpotentials coming from the reduced interfacial resistance and charge transfer resistance at both cathodes and anodes. The trench–wall CNT sponge simultaneously tackles the most critical problems on both the cathodes and anodes of Li‐S batteries, and this method can be utilized in designing new electrode materials for energy storage and beyond.     

Ultrathin MnO2/Graphene Oxide/Carbon Nanotube Interlayer as Efficient Polysulfide‐Trapping Shield for High‐Performance Li–S Batteries

Ultrathin MnO₂/graphene oxide/carbon nanotube (G/M@CNT) interlayers are developed as efficient polysulfide‐trapping shields for high‐performance Li–S batteries. A simple layer‐by‐layer procedure is used to construct a sandwiched vein–membrane interlayer of thickness 2 µm and areal density 0.104 mg cm^?2 by loading MnO₂ nanoparticles and graphene oxide (GO) sheets on superaligned carbon nanotube films. The G/M@CNT interlayer provides a physical shield against both polysulfide shuttling and chemical adsorption of polysulfides by MnO₂ nanoparticles and GO sheets. The synergetic effect of the G/M@CNT interlayer enables the production of Li–S cells with high sulfur loadings (60–80 wt%), a low capacity decay rate (?0.029% per cycle over 2500 cycles at 1 C), high rate performance (747 mA h g^?1 at a charge rate of 10 C), and a low self‐discharge rate with high capacity retention (93.0% after 20 d rest). Electrochemical impedance spectroscopy, cyclic voltammetry, and scanning electron microscopy observations of the Li anodes after cycling confirm the polysulfide‐trapping ability of the G/M@CNT interlayer and show its potential in developing high‐performance Li–S batteries.     

A Top‐Down Strategy toward 3D Carbon Nanosheet Frameworks Decorated with Hollow Nanostructures for Superior Lithium Storage

Graphene has shown great potential in vast fields due to the unique structure and properties, but its practical application is still hindered by high cost and scarcity in supply. The development of low‐cost substitute of graphene is thus highly desired to meet the practical demand of upcoming applications where extremely physical properties are not absolutely critical. In this work, a top‐down strategy for general synthesis of 3D carbon nanosheet frameworks decorated with metal nanoparticles by a metal nitrate‐assisted polymer‐blowing process is reported. Such architecture provides a promising structural platform for the fabrication of carbon nanosheet frameworks functionalized with metal oxide or carbon hollow nanostructures through subsequent chemical conversion. The unique structures impart intimate structural interconnectivities, highly opened freeway for ionic diffusion, large accessible surface area, as well as high structural stability, opening up a wide horizon for electrochemical applications, for example, high‐energy, long‐life lithium‐ion batteries and lithium–sulfur batteries highlighted in this work.     

Tailoring Rod‐Like FeSe2 Coated with Nitrogen‐Doped Carbon for High‐Performance Sodium Storage

Designing potential anodes for sodium‐ion battery with both remarkable durability and high‐rate capability has captured enormous attention so far. The engineering of size and morphology is deemed as an effective manner to boost the electrochemical properties. Owing to the anisotropic self‐assembly of iron selenide, rod‐like FeSe₂ coates with nitrogen‐doped carbon is prepared through the thermal reaction of Prussian blue with selenium. Notably, the cyano groups are effectively transformed into N‐doped carbon with Fe? N? C bonds, which uniformly coats FeSe₂, prompting Na⁺ transportations. Interestingly, the particle size is tailored by heating rates, along with increased carbon content, leading to broadened energy levels for redox reaction. Bestowed by these advantages, the FeSe₂/N‐C as Na‐storage anode delivers impressive electrochemical properties. Even at a rather high rate of 10.0 A g^?1, a considerable capacity of 308 mAh g^?1 is yielded over 10 000 loops. Supported by the detailed analysis of kinetic features, reduced size of particles could bring about the enhanced contributions of pseudocapacitive and quickening rate of ions transferring. The phase evolutions are further investigated by in situ EIS and ex‐situ technologies. The work is expected to provide a new strategy to prepare metal‐selenide with controllable size and induce the faster kinetic of high‐rate materials.     

High‐Performance Cathode Based on Self‐Templated 3D Porous Microcrystalline Carbon with Improved Anion Adsorption and Intercalation

Dual‐ion batteries (DIBs) have attracted much attention due to their advantages of low cost and especially environmental friendliness. However, the capacities of most DIBs are still unsatisfied (≈100 mAh g^?1) ascribed to the limited capacity of anions intercalation for conventional graphite cathode. In this study, 3D porous microcrystalline carbon (3D‐PMC) was designed and synthesized via a self‐templated growth approach, and when used as cathode for a DIB, it allows both intercalation and adsorption of anions. The microcrystalline carbon is beneficial to obtain capacity originated from anions intercalation, and the 3D porous structure with a certain surface area contributes to anions adsorption capacity. With the synergistic effect, this 3D‐PMC is utilized as cathode and tin as anode for a sodium‐based DIB, which has a high capacity of 168.0 mAh g^?1 at 0.3 A g^?1, among the best values of reported DIBs so far. This cell also exhibits long‐term cycling stability with a capacity retention of ≈70% after 2000 cycles at a high current rate of 1 A g^?1. It is believed that this work will provide a strategy to develop high‐performance cathode materials for DIBs.     

Tailoring 2D Heteroatom‐Doped Carbon Nanosheets with Dominated Pseudocapacitive Behaviors Enabling Fast and High‐Performance Sodium Storage

2D carbon nanosheets are considered to be promising candidates for use as sodium ion battery (SIB) anodes due to their large specific surface area and excellent electronic conductivity. However, their applications are hampered by inferior cycling performance, insufficient storage capacity, and high cost. N, B co‐doping carbon nanosheets (NBTs) are synthesized using biomass‐based gelatin as carbon precursor and boric acid as template, and demonstrate their great potential as high‐performance SIB anodes in practical applications. The synergistic effect of heteroatom doping and ultrathin 2D structure provides the NBTs with abundant defects, active sites, and short ion/electron transfer distance, which favors and improves the storage capabilities and rate performances. The optimized NBTs present a remarkable cyclability and superb rate capability (309 mAh g^?1 at 0.2 A g^?1 for 200 cycles; 225 mAh g^?1 at 1 A g^?1 for 2000 cycles). Meanwhile, the Na storage mechanism is proved to be a pseudocapacitive‐controlled process, which accounts for the fast charge/discharge behaviors. This work demonstrates an effective template method to produce 2D heteroatoms co‐doping carbon nanosheets to achieve excellent Na storage performances.     

Single‐Walled Carbon Nanotube/Phase Change Material Composites: Sunlight‐Driven,Reversible, Form‐Stable Phase Transitions for Solar Thermal Energy Storage

The development of solar energy conversion materials is critical to the growth of a sustainable energy infrastructure in the coming years. A novel hybrid material based on single‐walled carbon nanotubes (SWNTs) and form‐stable polymer phase change materials (PCMs) is reported. The obtained materials have UV‐vis sunlight harvesting, light‐thermal conversion, thermal energy storage, and form‐stable effects. Judicious application of this efficient photothermal conversion to SWNTs has opened up a rich field of energy materials based on novel SWNT/PCM composits with enhanced performance in energy conversion and storage.     

Facile Spraying Synthesis and High‐Performance Sodium Storage of Mesoporous MoS2/C Microspheres

A facile one‐step spraying synthesis of MoS₂/C microspheres and their enhanced electrochemical performance as anode of sodium‐ion batteries is reported. An aerosol spraying pyrolysis without any template is employed to synthesize MoS₂/C microspheres, in which ultrathin MoS₂ nanosheets (≈2 nm) with enlarged interlayers (≈0.64 nm) are homogeneously embedded in mesoporous carbon microspheres. The as‐synthesized mesoporous MoS₂/C microspheres with 31 wt% carbon have been applied as an anode material for sodium ion batteries, demonstrating long cycling stability (390 mAh g^?1 after 2500 cycles at 1.0 A g^?1) and high rate capability (312 mAh g^?1 at 10.0 A g^?1 and 244 mAh g^?1 at 20.0 A g^?1). The superior electrochemical performance is due to the uniform distribution of ultrathin MoS₂ nanosheets in mesoporous carbon frameworks. This kind of structure not only effectively improves the electronic and ionic transport through MoS₂/C microspheres, but also minimizes the influence of pulverization and aggregation of MoS₂ nanosheets during repeated sodiation and desodiation.     

In Situ Construction of 3D Interconnected FeS@Fe3C@Graphitic Carbon Networks for High‐Performance Sodium‐Ion Batteries

Iron sulfides have been attracting great attention as anode materials for high‐performance rechargeable sodium‐ion batteries due to their high theoretical capacity and low cost. In practice, however, they deliver unsatisfactory performance because of their intrinsically low conductivity and volume expansion during charge–discharge processes. Here, a facile in situ synthesis of a 3D interconnected FeS@Fe₃C@graphitic carbon (FeS@Fe₃C@GC) composite via chemical vapor deposition (CVD) followed by a sulfuration strategy is developed. The construction of the double‐layered Fe₃C/GC shell and the integral 3D GC network benefits from the catalytic effect of iron (or iron oxides) during the CVD process. The unique nanostructure offers fast electron/Na ion transport pathways and exhibits outstanding structural stability, ensuring fast kinetics and long cycle life of the FeS@Fe₃C@GC electrodes for sodium storage. A similar process can be applied for the fabrication of various metal oxide/carbon and metal sulfide/carbon electrode materials for high‐performance lithium/sodium‐ion batteries.     

Understanding the Charge Storage Mechanism to Achieve High Capacity and Fast Ion Storage in Sodium‐Ion Capacitor Anodes by Using Electrospun Nitrogen‐Doped Carbon Fibers

Microporous nitrogen‐rich carbon fibers (HAT‐CNFs) are produced by electrospinning a mixture of hexaazatriphenylene‐hexacarbonitrile (HAT‐CN) and polyvinylpyrrolidone and subsequent thermal condensation. Bonding motives, electronic structure, content of nitrogen heteroatoms, porosity, and degree of carbon stacking can be controlled by the condensation temperature due to the use of the HAT‐CN with predefined nitrogen binding motives. The HAT‐CNFs show remarkable reversible capacities (395 mAh g^?1 at 0.1 A g^?1) and rate capabilities (106 mAh g^?1 at 10 A g^?1) as an anode material for sodium storage, resulting from the abundant heteroatoms, enhanced electrical conductivity, and rapid charge carrier transport in the nanoporous structure of the 1D fibers. HAT‐CNFs also serve as a series of model compounds for the investigation of the contribution of sodium storage by intercalation and reversible binding on nitrogen sites at different rates. There is an increasing contribution of intercalation to the charge storage with increasing condensation temperature which becomes less active at high rates. A hybrid sodium‐ion capacitor full cell combining HAT‐CNF as the anode and salt‐templated porous carbon as the cathode provides remarkable performance in the voltage range of 0.5–4.0 V (95 Wh kg^?1 at 0.19 kW kg^?1 and 18 Wh kg^?1 at 13 kW kg^?1).     

Confined Volume Change in Sn‐Co‐C Ternary Tube‐in‐Tube Composites for High‐Capacity and Long‐Life Lithium Storage

All high capacity Li‐alloy anodes for Li‐ion battery suffer from enormous volume expansion and extraction during the lithium‐ion insertion and extraction process. A Sn‐Co‐CNT@CNT ternary tube‐in‐tube nanostructure is prepared by an in situ template technique and shows perfect structure suitability to solve the critical volume change problem. The morphology, size, and quantity of the filled CNT‐supported Sn‐Co nanoparticles can be also tuned by adjusting the experimental conditions to achieve optimal electrochemical performances. The tube‐in‐tube product exhibits larger‐than‐theoretical reversible capacities of 890–811 mA h g^?1 at 0.1C in 200 cycles and excellent rate capability and high‐rate cycling stability. The excellent electrochemical performance is mainly attributed to the confined volume change in the nanotube cavities and ensured permanent electrical connectivity of the immobilized Sn‐Co anodes.     

Lithium Ion Breathable Electrodes with 3D Hierarchical Architecture for Ultrastable and High‐Capacity Lithium Storage

Transition‐metal oxides show genuine potential in replacing state‐of‐the‐art carbonaceous anode materials in lithium‐ or sodium‐ion batteries because of their much higher theoretical capacity. However, they usually undergo massive volume change, which leads to numerous problems in both material and electrode levels, such as material pulverization, instable solid‐electrolyte interphase, and electrode failure. Here, it is demonstrated that lithium‐ion breathable hybrid electrodes with 3D architecture tackle all these problems, using a typical conversion‐type transition‐metal oxide, Fe₃O₄, of which nanoparticles are anchored onto 3D current collectors of Ni nanotube arrays (NTAs) and encapsulated by δ‐MnO₂ layers (Ni/Fe₃O₄@MnO₂). The δ‐MnO₂ layers reversibly switch lithium insertion/extraction of internal Fe₃O₄ nanoparticles and protect them against pulverizing and detaching from NTA current collectors, securing exceptional integrity retention and efficient ion/electron transport. The Ni/Fe₃O₄@MnO₂ electrodes exhibit superior cyclability and high‐capacity lithium storage (retaining ≈1450 mAh g^?1, ≈96% of initial value at 1 C rate after 1000 cycles).     

Trimetallic Mn‐Fe‐Ni Oxide Nanoparticles Supported on Multi‐Walled Carbon Nanotubes as High‐Performance Bifunctional ORR/OER Electrocatalyst in Alkaline Media

Discovering precious metal‐free electrocatalysts exhibiting high activity and stability toward both the oxygen reduction (ORR) and the oxygen evolution (OER) reactions remains one of the main challenges for the development of reversible oxygen electrodes in rechargeable metal–air batteries and reversible electrolyzer/fuel cell systems. Herein, a highly active OER catalyst, Fe_0.3Ni_0.7O_X supported on oxygen‐functionalized multi‐walled carbon nanotubes, is substantially activated into a bifunctional ORR/OER catalyst by means of additional incorporation of MnO_X. The carbon nanotube‐supported trimetallic (Mn‐Ni‐Fe) oxide catalyst achieves remarkably low ORR and OER overpotentials with a low reversible ORR/OER overvoltage of only 0.73 V, as well as selective reduction of O₂ predominantly to OH^?. It is shown by means of rotating disk electrode and rotating ring disk electrode voltammetry that the combination of earth‐abundant transition metal oxides leads to strong synergistic interactions modulating catalytic activity. The applicability of the prepared catalyst for reversible ORR/OER electrocatalysis is evaluated by means of a four‐electrode configuration cell assembly comprising an integrated two‐layer bifunctional ORR/OER electrode system with the individual layers dedicated for the ORR and the OER to prevent deactivation of the ORR activity as commonly observed in single‐layer bifunctional ORR/OER electrodes after OER polarization.