Encapsulation of MoSe2 in carbon fibers as anodes for potassium ion batteries and nonaqueous battery-supercapacitor hybrid devices

Defect Engineering of Hexagonal MAB Phase Ti2InB2 as Anode of Lithium-Ion Battery with Excellent Cycling Stability

Hexagonal MAB phases （h-MAB） have attracted attention due to their potential to exfoliate into MBenes, similar to MXenes, which are predicted to be promising for Li-ion battery applications. However, the high cost of synthesizing MBenes poses challenges for their use in batteries. This study presents a novel approach where a simple ball-milling treatment is employed to enhance the purity of the h-MAB phase Ti2InB2 and introduce significant indium defects, resulting in improved conductivity and the creation of abundant active sites. The synthesized Ti2InB2 with indium defects (VIn-Ti2InB2) exhibits excellent electrochemical properties, particularly exceptional long-cycle stability at current densities of 5 A g-1 (5000 cycles, average capacity decay of 0.0018%) and 10 A g-1 (15 000 cycles, average capacity decay of 0.093%). The charge storage mechanism of VIn-Ti2InB2, involving a dual redox reaction, is proposed, where defects promote the In-Li alloy reaction and a redox reaction with Li in the TiB layer. Finally, a Li-ion full cell demonstrates cycling stability at 0.5 A g-1 after 350 cycles. This work presents the first accessible and scalable application of VIn-Ti2InB2 as a Li-ion anode, unlocking a wealth of possibilities for sustainable electrochemical applications of h-MAB phases.

Electronic properties of MoSe2 nanowrinkles

Mechanical deformations, either spontaneously occurring during sample preparation or purposely induced in their nanoscale manipulation, drastically affect the electronic and optical properties of transition metal dichalcogenide monolayers. In this first-principles work based on density-functional theory, we shed light on the interplay among strain, curvature, and electronic structure of MoSe2 nanowrinkles. We analyze their structural properties highlighting the effects of coexisting local domains of tensile and compressive strain in the same system. By contrasting the band structures of the nanowrinkles against counterparts obtained for flat monolayers subject to the same amount of strain, we clarify that the specific features of the former, such as the moderate variation of the band-gap size and its persisting direct nature, are ruled by curvature rather than strain. The analysis of the wave-function distribution indicates strain-dependent localization of the frontier states in the conduction region while in the valence, the sensitivity to strain is much less pronounced. The discussion about transport properties, based on inspection of the effective masses, reveals excellent perspectives for these systems as active components for (opto)electronic devices.

Bond modulation of MoSe2+x driving combined intercalation and conversion reactions for high-performance K cathodes

The urgent demand for large-scale global energy storage systems and portable electronic devices is driving the need for considerable energy density and stable batteries. Here, Se atoms are introduced between MoSe₂ layers (denoted as MoSe_2+x ) by bond modulation to produce a high-performance cathode for potassium-ion batteries. The introduced Se atoms form covalent Se-Se bonds with the Se in MoSe₂, and the advantages of bond modulation are as follows: (i) the interlayer spacing is enlarged which increases the storage space of K⁺; (ii) the system possesses a dual reaction mechanism, and the introduced Se can provide an additional conversion reaction when discharged to 0.5 V, which improves the capacity further; (iii) the Se atoms confined between MoSe₂ layers do not give rise to the shuttle effect. MoSe_2+x is compounded with rGO (MoSe_2+x -rGO) as a cathode for potassium-ion batteries and displays an ultrahigh capacity (235 mA h g^-1 at 100 mA g^-1), a long cycle life (300 cycles at 100 mA g^-1) and an extraordinary rate performance (135 mA h g^-1 at 1000 mA g^-1 and 89 mA h g^-1 at 2000 mA g^-1). Pairing the MoSe_2+x -rGO cathode with graphite, the full cell delivers considerable energy density compared to other K cathode materials. The MoSe_2+x -rGO cathode also exhibits excellent electrochemical performance for lithium-ion batteries. This study on bond modulation driving combined intercalation and conversion reactions offers new insights into the design of high-performance K cathodes.

Exploring 2D Energy Storage Materials: Advances in Structure, Synthesis, Optimization Strategies, and Applications for Monovalent and Multivalent Metal-Ion Hybrid Capacitors

The design and development of advanced energy storage devices with good energy/power densities and remarkable cycle life has long been a research hotspot. Metal-ion hybrid capacitors (MHCs) are considered as emerging and highly prospective candidates deriving from the integrated merits of metal-ion batteries with high energy density and supercapacitors with excellent power output and cycling stability. The realization of high-performance MHCs needs to conquer the inevitable imbalance in reaction kinetics between anode and cathode with different energy storage mechanisms. Featured by large specific surface area, short ion diffusion distance, ameliorated in-plane charge transport kinetics, and tunable surface and/or interlayer structures, 2D nanomaterials provide a promising platform for manufacturing battery-type electrodes with improved rate capability and capacitor-type electrodes with high capacity. In this article, the fundamental science of 2D nanomaterials and MHCs is first presented in detail, and then the performance optimization strategies from electrodes and electrolytes of MHCs are summarized. Next, the most recent progress in the application of 2D nanomaterials in monovalent and multivalent MHCs is dealt with. Furthermore, the energy storage mechanism of 2D electrode materials is deeply explored by advanced characterization techniques. Finally, the opportunities and challenges of 2D nanomaterials-based MHCs are prospected.

Advances and challenges in metal selenides enabled by nanostructures for electrochemical energy storage applications

The development of nanomaterials and their related electrochemical energy storage (EES) devices can provide solutions for improving the performance and development of existing EES systems owing to their high electronic conductivity and ion transport and abundant embeddable sites. Recent progress has demonstrated that metal selenides are attracting increasing attention in the field of EES because of their unique structures, high theoretical capacities, rich element resources, and high conductivity. However, there are still many challenges in their application in EES, and thus the use of nanoscale metal selenide materials in commercial devices is limited. In this review, we summarize recent advances in the nanostructured design of metal selenides (e.g., zero-, one-, two-, and three-dimensional, and self-supported structures) and present their advantages in terms of EES performance. Moreover, some remarks on the potential challenges and research prospects of nanostructured metal selenides in the field of EES are presented.

Recent Advancements in Chalcogenides for Electrochemical Energy Storage Applications

Energy storage has become increasingly important as a study area in recent decades. A growing number of academics are focusing their attention on developing and researching innovative materials for use in energy storage systems to promote sustainable development goals. This is due to the finite supply of traditional energy sources, such as oil, coal, and natural gas, and escalating regional tensions. Because of these issues, sustainable renewable energy sources have been touted as an alternative to nonrenewable fuels. Deployment of renewable energy sources requires efficient and reliable energy storage devices due to their intermittent nature. High-performance electrochemical energy storage technologies with high power and energy densities are heralded to be the next-generation storage devices. Transition metal chalcogenides (TMCs) have sparked interest among electrode materials because of their intriguing electrochemical properties. Researchers have revealed a variety of modifications to improve their electrochemical performance in energy storage. However, a stronger link between the type of change and the resulting electrochemical performance is still desired. This review examines the synthesis of chalcogenides for electrochemical energy storage devices, their limitations, and the importance of the modification method, followed by a detailed discussion of several modification procedures and how they have helped to improve their electrochemical performance. We also discussed chalcogenides and their composites in batteries and supercapacitors applications. Furthermore, this review discusses the subject’s current challenges as well as potential future opportunities.

N, P Codoped Hollow Carbon Nanospheres Decorated with MoSe2 Ultrathin Nanosheets for Efficient Potassium-Ion Storage

Potassium-ion batteries (KIBs) are gradually being considered as an alternative for lithium-ion batteries because of their non-negligible advantages such as abundance and low expenditure of K, as well as higher electrochemical potential than another alternative─sodium-ion batteries. Nevertheless, when the electrode materials are inserted and extracted with large-sized K⁺ ions, the tremendous volume change will cause the collapse of the microstructures of electrodes and make the charging/discharging process irreversible, thus disapproving their extended application. In response to this, we put forward a feasible strategy to realize the in situ assembly of layered MoSe₂ nanosheets onto N, P codoped hollow carbon nanospheres (MoSe₂/NP-HCNSs) through thermal annealing and heteroatom doping strategies, and the resulting nanoengineered material can function well as an anode for KIBs. This cleverly designed nanostructure of MoSe₂/NP-HCNS can broaden the interlayer spacing of MoSe₂ to boost the efficiency of the insertion/extraction of K ions and also can accommodate large volume change-caused mechanical strain, facilitate electrolyte penetration, and prevent the aggregation of MoSe₂ nanosheets. This synthetic method generates abundant defects to increase the amounts of active sites, as well as conductivity. The hierarchical nanostructure can effectively increase the proportion of pseudo-capacitance and promote interfacial electronic transfer and K⁺ diffusion, thus imparting great electrochemical performance. The MoSe₂/NP-HCNS anode exhibits a high reversible capacity of 239.9 mA h g^-1 at 0.1 A g^-1 after 200 cycles and an ultralong cycling life of 161.1 mA h g^-1 at 1 A g^-1 for a long period of 1000 cycles. This nanoengineering method opens up new insights into the development of promising anode materials for KIBs.

Rational Design of Unique MoSe2-Carbon Nanobowl Particles Endows Superior Alkali Metal-Ion Storage Beyond Lithium

Attracted by the rich earth abundance and low-cost advantages, alkali metal-ion (Na/K)-based energy storage devices have attracted wide interest as promising candidates for energy economizing in recent years. Unfortunately, the lack of suitable host materials with high capacity and long life span for alkali metal-ion storage has severely impeded their practical application in large-scale energy storage devices. Herein, we present a promising anode candidate composed of ultrasmall MoSe₂ clusters embedded in a nitrogen-doped hollow carbon nanobowl substrate to form unique MoSe₂-Carbon nanobowl particles (denoted as MoSe₂⊂CNB). MoSe₂⊂CNB demonstrates exceptional electrochemical properties for alkali metal-ion storage including sodium and potassium. In situ Raman spectroscopy and galvanostatic intermittent titration measurements reveal the possible reason for the high performance of MoSe₂⊂CNB. Notably, the assembled potassium-ion hybrid capacitors could manifest an extraordinary energy density of 130.7 W h kg^-1 at 0.2 A g^-1, a high power density of 13,607 W kg^-1, and an enviable cycle life after 6000 cycles, further reflecting the great developmental potential for energy storage devices in practical applications. This work provides a new method to design functional nanostructures for electrode materials to drive the development and application of possible energy storage devices.

Recent Advances and Perspectives of Battery-Type Anode Materials for Potassium Ion Storage

Potassium ion energy storage devices are competitive candidates for grid-scale energy storage applications owing to the abundancy and cost-effectiveness of potassium (K) resources, the low standard redox potential of K/K⁺, and the high ionic conductivity in K-salt-containing electrolytes. However, the sluggish reaction dynamics and poor structural instability of battery-type anodes caused by the insertion/extraction of large K⁺ ions inhibit the full potential of K ion energy storage systems. Extensive efforts have been devoted to the exploration of promising anode materials. This Review begins with a brief introduction of the operation principles and performance indicators of typical K ion energy storage systems and significant advances in different types of battery-type anode materials, including intercalation-, mixed surface-capacitive-/intercalation-, conversion-, alloy-, mixed conversion-/alloy-, and organic-type materials. Subsequently, host-guest relationships are discussed in correlation with the electrochemical properties, underlying mechanisms, and critical issues faced by each type of anode material concerning their implementation in K ion energy storage systems. Several promising optimization strategies to improve the K⁺ storage performance are highlighted. Finally, perspectives on future trends are provided, which are aimed at accelerating the development of K ion energy storage systems.

Confining MoSe2 Nanosheets into N-Doped Hollow Porous Carbon Microspheres for Fast-Charged and Long-Life Potassium-Ion Storage

The potassium-ion battery (PIB) is the most promising alternative to a lithium-ion battery (LIB). Exploitation of a suitable electrode material is crucial to promote the development of PIBs. The MoSe₂ material has attracted much attention due to its high theoretical capacity, unique layered structure, and good conductivity. However, the potassium storage property of MoSe₂ has been suffering from structural fragmentation and sluggish reaction kinetic caused by large potassium ions upon insertion/extraction, which needs to be further improved. Herein, the MoSe₂ nanosheets are confined into N-doped hollow porous carbon microspheres (MoSe₂@N-HCS) by spray drying and high-temperature selenization. It delivers a superior rate performance of 113.7 mAh g^-1 at 10 A g^-1 and remains at a high capacity of 158.3 mAh g^-1 at 2 A g^-1 even after 16 700 cycles for PIBs. The excellent electrochemical performance can be attributed to unique structure, N-doping, and robust chemical bonds. The storage mechanism of MoSe₂ for potassium ions was explored. The outstanding properties of MoSe₂@N-HCS make it a promising anode material for PIBs.

Research progress in transition metal chalcogenide based anodes for K-ion hybrid capacitor applications: a mini-review

Metal ion capacitors have gained a lot of interest as a new kind of capacitor-battery hybrid energy storage system because of their high power density while maintaining energy density and a long lifetime. Potassium ion hybrid capacitors (PIHCs) have been suggested as possible alternatives to lithium-ion/sodium-ion capacitors because of the plentiful potassium supplies, and their lower standard electrode potential and low cost. However, due to the large radius of the potassium ion, PIHCs also face unsatisfactory reaction kinetics, low energy density, and short lifespan. Recently, transition metal chalcogenide (TMC)-based materials with distinctive structures and fascinating characteristics have been considered an emerging candidate for PIHCs, owing to their unique physical and chemical properties. This mini-review mainly focuses on the recent research progress on TMC-based materials for the PIHC applications summarized. Finally, the existing challenges and perspectives are given to improve further and construct advanced TMC-based electrode materials.

Metal ion capacitors have gained a lot of interest as a new kind of capacitor-battery hybrid energy storage system because of their high power density while maintaining energy density and a long lifetime.

Fabrication of CoSe@NC nanocubes for high performance potassium ion batteries

Potassium-ion batteries (PIBs) are considered as a promising candidate for large-scale energy storage. While exploring suitable anode materials are of vital need for the practical applications of PIBs. Herein, a well-designed heterostructured anode material CoSe nanocubes wrapped by N-doped carbon (CoSe@NC), has been successfully fabricated by simple annealing ZIF-67 nanocubes followed by in-situ selenization process. It is noted that ZIF-67 nanocubes are used as an effective template for the formation of porous structure, which can facilitate the construction of heterogeneous interface between CoSe and N-doped carbon (NC), effectively stabilizing CoSe with conversion reaction product Co⁰, increasing the diffusion mobility of electrons and K⁺-ions, and alleviating huge volume change. As expected, the heterostructured CoSe@NC nanocubes exhibit excellent K⁺-storage performance, which can display a rather high initial charge capacity (388.7 mAh g^-1 at 0.1 A g^-1 with the columbic efficiency of 70%), superior cyclic stability (309.6 mA h g^-1 after 500 cycles at 2 A g^-1), and exceptional rate capability (365.9 mAh g^-1 at 2 A g^-1). In terms of the low-cost and facile production approach for CoSe@NC, which makes the CoSe@NC a promising anode material for PIBs.

Application of 2D Materials to Potassium-Ion Hybrid Capacitors

Metal-ion hybrid supercapacitors (MICs) are a new type of electrochemical energy storage (EES) device, consisting of a battery-type electrode and a supercapacitor (SC)-type electrode. Exhibiting the advantages of both batteries and SCs (e. g., good energy density, excellent power density and long cycle life), these advanced energy storage devices have considerable commercial application prospects. Among MICs, potassium-ion hybrid supercapacitors (PICs) have several further advantages, including abundancy of resources, low standard electrode potential, and low cost. PICs are regarded as potential substitutes for lithium- or sodium-ion hybrid supercapacitors. However, the practical applications of PICs remain limited, owing to the imbalance of kinetics and capacity between the electrodes, the slow ion/electron diffusion rate, and the poor electrode structural stability. Recently, 2D materials with distinct structures and fascinating features have elicited widespread attention for application in PICs, thus achieving significant enhancements, ranging from charge storage capacity to reaction kinetics. This Review discusses research progress in 2D materials for PICs. Firstly, the energy storage principle and development requirements of MICs are introduced. The pivotal advantages and significant roles of 2D materials in the fabrication of PICs are then discussed in detail. Lastly, the challenges and prospects of the application of 2D materials to high-performance PICs are presented.

Recent progress in electrochemical performance of binder-free anodes for potassium-ion batteries

Potassium ion batteries (PIBs) are regarded as one of the most promising candidates for large-scale stationary energy storage beyond lithium-ion batteries (LIBs), owing to the abundance of potassium resources and low cost. Unfortunately, the practical application of PIBs is severely restricted by their poor rate capacity and unsatisfactory cycle performance. In traditional electrodes, a binder usually plays an important role in integrating individual active materials with conductive additives. Nevertheless, binders are not only generally electrochemically inactive but also insulating, which is unfavorable for improving overall energy density and cycling stability. To this end, in terms of both improved electronic conductivity and electrochemical reaction reversibility, binder-free electrodes offer great potential for high-performance PIBs. Moreover, the anode is a crucial configuration to determine full cell electrochemical performance. Therefore, this review analyzes in detail the electrochemical properties of the different type binder-free anodes, including carbon-based substrates (graphene, carbon nanotubes, carbon nanofibers, and so on), MXene-based substrates and metal-based substrates (Cu and Ni). More importantly, the recent progress, critical issues, challenges, and perspectives in binder-free electrodes for PIBs are further discussed. This review will provide theoretical guidance for the synthesis of high-performance anode materials and promote the further development of PIBs.

Ultrafine ZnS Nanoparticles in the Nitrogen-Doped Carbon Matrix for Long-Life and High-Stable Potassium-Ion Batteries

Potassium-ion batteries (KIBs) have attracted researchers' widespread attention because of the luxuriant reserves of potassium salts and their low cost. Nevertheless, the absence of suitable electrode materials with a stable electrochemical property is a crucial issue, which seriously hampers the practical applications of KIBs. Herein, a scalable anode material consisting of ultrafine ZnS nanoparticles encapsulated in three-dimensional (3D) carbon nanosheets is explored for KIBs. This hierarchical anode is obtained via a simple and universal sol-gel method combined with a typical solid-phase sulfidation route. The special structure of this anode facilitates good contact with electrolytes and has enough voids to buffer the large volumetric stress changing during K⁺ insertion/extraction. Thus, the 3D ZnS@C electrode exhibitsour stable cycling performance (230 mAh g^-1 over 2300 cycles at 1.0 A g^-1) and superior rate capability. The kinetic analysis indicates that a ZnS@C anode with considerable pesoudecapactive contribution benefits a fast potassium/depotassium process. Detailed ex-situ and in-situ measurements reveal that this ZnS@C anode combines reversible conversion and alloying-type reactions. This rationally designed ZnS@C material is highly applicable for KIBs, and the current route opens an avenue for the development of highly stable K⁺ storage materials.

High potassium ion storage capacity with long cycling stability of sustainable oxygen-rich carbon nanosheets

The development of carbon materials for potassium storage is limited by their low specific capacity and poor cycling stability due to the sluggish kinetics of K ions. Herein, fucoidan-derived oxygen-rich carbon nanosheets are reported as a fantastic anode for potassium ion batteries. Attributed to its 2D porous sheet-like structure (morphology engineering), rich oxygen doping (defect engineering), and dilated graphitic layer in an amorphous structure (structure engineering), a competitive capacity of 392 mA h g-1 at 0.05 A g-1 and a long cycling span over 2500 cycles at 2 A g-1 was achieved for the carbon anode, outperforming most of the reported carbons. The kinetic analyses reveal that rich active sites and a porous nanosheet structure account for the superb rate performance and cycling stability of the material. Ex situ X-ray photoelectron spectroscopy measurements demonstrate that the introduction of C[double bond, length as m-dash]O greatly promotes K+ adsorption, and that the improvement of the C[double bond, length as m-dash]O bonds during cycling contributes to enhancement in the capacity. The fabricated potassium ion hybrid capacitor displays an exceptional energy/power density of 193 W h kg-1/22 324 W kg-1, and a promising cycling stability with 99.3% capacity retention over 2000 cycles. This work provides a large-scale synthesis strategy for preparing oxygen-rich carbon nanosheets for advanced potassium ion storage.

Bismuth selenide nanosheets confined in thin carbon layers as anode materials for advanced potassium-ion batteries

A composite of Bi2Se3 nanosheets confined in ultrathin carbon layers is synthesized. The carbon layers buffer the volume variation and enhance the electronic conductivity of the electrode, resulting in improved potassium-ion storage performance.

Emerging Potassium-ion Hybrid Capacitors

As a new type of capacitor-battery hybrid energy storage device, metal-ion capacitors have attracted widespread attention because of their high-power density while ensuring energy density and long lifespan. Potassium-ion capacitors (KICs) featuring the merits of abundant potassium resources, lower standard electrode potential, and low cost have been considered as potential alternatives to lithium-/sodium-ion capacitors. However, KICs still face issues including unsatisfactory reaction kinetics, low energy density, and poor lifetime owing to the large radius of the potassium ion. In this Review, the importance of emerging potassium-ion capacitor is addressed. The Review offers a brief discussion of the fundamental working principle of KICs, along with an overview of recent advances and achievements of a variety of electrode materials for dual carbon and non-dual carbon KICs. Furthermore, electrolyte chemistry, binders as well as electrode/electrolyte interface, are summarized. Finally, existing challenges and perspectives on further development of KICs are also presented.

Recent progress in sodium/potassium hybrid capacitors

Metal ion hybrid capacitors (MIHCs) have been recognized as one of the most promising power sources owing to their combined merits of high energy density in batteries and high power output in supercapacitors. The kinetics mismatch between the capacitor-type cathode and battery-type anode yet must be well addressed before implementing their practical feasibility. Here, we overview the recent progress in sodium and potassium ion hybrid capacitors (SIHCs and PIHCs) and discuss the major challenges and give an outlook on the future directions in this field. The fundamental knowledge and the history will be firstly introduced, and special emphasis is then laid on the development of a variety of electrode materials in recent years. The prospects of future research of MIHCs are finally proposed towards their practical applications. We wish that this feature article can not only educate newcomers starting their reasearch in this field, but also inspire experieced researchers to contribute to the development of high-performance MIHC devices.

Enhancing the Performance of a Battery-Supercapacitor Hybrid Energy Device Through Narrowing the Capacitance Difference Between Two Electrodes via the Utilization of 2D MOF-Nanosheet-Derived Ni@Nitrogen-Doped-Carbon Core-Shell Rings as Both Negative and Positive Electrodes

Narrowing the capacitance gap between the positive and negative electrodes for the enhancement of the energy densities of battery-supercapacitor hybrid (BSH) devices is urgent and very important. Herein, a new strategy to synchronously improve the positive-negative system and reduce the capacitance discrepancies between two electrodes through the utilization of the same MOF-based precursors ([Ni(ATA)₂(H₂O)₂](H₂O)₃) has been proposed. Nickel/nitrogen codoped carbon (Ni@NC) materials, serving as positive electrodes, deliver battery-type behavior with the enhancement of capacities, which are even superior to those of pristine carbon-based materials with large surface areas. Meanwhile, HCl-treated Ni@NC materials (named A-Ni@NC) are employed as negative electrodes within the potential window of -1 to 0 V and exhibit higher capacitances than that of the commercial activated carbon. With Ni@NC and A-Ni@NC as positive and negative electrodes in BSH devices, the as-fabricated cells display higher capacities and energy densities, more excellent cycling stability, and far superior capacity retention in comparison with those of Ni@NC//AC cells. These results clearly confirm that our strategy is successful and effective.

K2Ti6O13/carbon core-shell nanorods as a superior anode material for high-rate potassium-ion batteries

Bunches of oriented K2Ti6O13 nanorods coated by a thin carbon layer (4-7 nm) were prepared by combining hydrothermal and heat treatment in sequence. The K2Ti6O13 nanorods possess long- and short-axis crystal orientations of <010> and <001>, respectively, contributing to fast K+ diffusion, and the carbon-coating layer improves the electron conductivity. In addition, the obtained K2Ti6O13/carbon has a high compaction density, which is beneficial for realizing high volumetric specific capacity. When evaluated as a potassium-ion battery anode, the nanorods demonstrated a superior rate capability (122.5, 104.3, 92.3, 78.6 and 65.1 mA h g-1 at current densities of 20, 50, 100, 200 and 500 mA g-1, respectively), a favourable cycle life (118.5 mA h g-1 at 25 mA g-1 for 200 cycles) and high capacity retention.

Heterostructures of 2D Molybdenum Dichalcogenide on 2D Nitrogen-Doped Carbon: Superior Potassium-Ion Storage and Insight into Potassium Storage Mechanism

Constructing 2D heterostructure materials by stacking different 2D materials can combine the merits of the individual building blocks while eliminating their shortcomings. Dichalcogenides are attractive anodes for potassium-ion batteries (KIBs) due to their high theoretical capacity. However, the practical application of dichalcogenide is greatly hampered by the poor electrochemical performance due to sluggish kinetics of K⁺ insertion and the electrode structure collapse resulting from the large K⁺ insertion. Herein, heterostructures of 2D molybdenum dichalcogenide on 2D nitrogen-doped carbon (MoS₂ , MoSe₂ -on-NC) are prepared to boost their potassium storage performance. The unique 2D heterostructures possess built-in heterointerfaces, facilitating K⁺ diffusion. The robust chemical bonds (CS, CSe, CMo bonds) enhance the mechanical strength of electrodes, thus suppressing the volume expansion. The 2D N-doped carbon nanosheets interconnected as a 3D structure offer a fast diffusion path for electrons. Benefitting from these merits, both the MoS₂ -on-NC and the MoSe₂ -on-NC exhibit unprecedented cycle life. Moreover, the electrochemical reaction mechanism of MoSe₂ is revealed during the process of potassiation and depotassiation.

Cocoon Silk-Derived, Hierarchically Porous Carbon as Anode for Highly Robust Potassium-Ion Hybrid Capacitors

Potassium-ion hybrid capacitors (KIHCs) have attracted increasing research interest because of the virtues of potassium-ion batteries and supercapacitors. The development of KIHCs is subject to the investigation of applicable K+ storage materials which are able to accommodate the relatively large size and high activity of potassium. Here, we report a cocoon silk chemistry strategy to synthesize a hierarchically porous nitrogen-doped carbon (SHPNC). The as-prepared SHPNC with high surface area and rich N-doping not only offers highly efficient channels for the fast transport of electrons and K ions during cycling, but also provides sufficient void space to relieve volume expansion of electrode and improves its stability. Therefore, KIHCs with SHPNC anode and activated carbon cathode afford high energy of 135 Wh kg-1 (calculated based on the total mass of anode and cathode), long lifespan, and ultrafast charge/slow discharge performance. This study defines that the KIHCs show great application prospect in the field of high-performance energy storage devices.

An in situ electrospinning route to fabricate NiO-SnO2 based detectors for fast H2S sensing

Hydrogen sulfide (H₂S) is a toxic and flammable chemical, even in low concentration. In this study, an in situ electrospinning strategy was developed to directly deposit the sensitive materials of nickel oxide (NiO)-doped SnO₂ nanofiber on alumina substrates, resulting in the fast H₂S detection. The electrospun fiber could be deposited on to the alumina tube directly, and remain there during calcination. Using this method, the NiO-doped SnO₂ nanofibers fabricated and manifested a fast response, fast recovery, and high selectivity at a low temperature (150 °C). A 15% atom NiO-doped SnO₂ nanofiber-containing H₂S detector presented a high response (1352), low response time (23 s), and low recovery time (38 s) while detecting a concentration of 50 ppm H₂S at 150 °C. Compared to conventional methods, the H₂S detector based on the in situ electrospinning method showed a higher sensitivity, faster response, and faster recovery. Furthermore, the superior performance of the detector can be ascribed to the thinner film and non-interrupted fiber structure. Additionally, the transformation of NiO to Ni₃S₂, confirmed by the x-ray photoelectron spectroscopy under a H₂S atmosphere, suggested the main reason for the detector's high performance. The high performance of the NiO-doped SnO₂ suggests a strategy for gas detectors, biodetectors, and semiconductor devices.

Two-Dimensional Transition Metal Chalcogenides for Alkali Metal Ions Storage

On the heels of exacerbating environmental concerns and ever-growing global energy demand, development of high-performance renewable energy-storage and -conversion devices has aroused great interest. The electrode materials, which are the critical components in electrochemical energy storage (EES) devices, largely determine the energy-storage properties, and the development of suitable active electrode materials is crucial to achieve efficient and environmentally friendly EES technologies albeit the challenges. Two-dimensional transition-metal chalcogenides (2D TMDs) are promising electrode materials in alkali metal ion batteries and supercapacitors because of ample interlayer space, large specific surface areas, fast ion-transfer kinetics, and large theoretical capacities achieved through intercalation and conversion reactions. However, they generally suffer from low electronic conductivities as well as substantial volume change and irreversible side reactions during the charge/discharge process, which result in poor cycling stability, poor rate performance, and low round-trip efficiency. In this Review, recent advances of 2D TMDs-based electrode materials for alkali metal-ion energy-storage devices with the focus on lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), potassium-ion batteries (PIBs), high-energy lithium-sulfur (Li-S), and lithium-air (Li-O₂ ) batteries are described. The challenges and future directions of 2D TMDs-based electrode materials for high-performance LIBs, SIBs, PIBs, Li-S, and Li-O₂ batteries as well as emerging alkali metal-ion capacitors are also discussed.

Three-Dimensional Self-assembled Hairball-Like VS4 as High-Capacity Anodes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are considered to be attractive candidates for large-scale energy storage systems because of their rich earth abundance and consistent performance. However, there are still challenges in developing desirable anode materials that can accommodate rapid and stable insertion/extraction of Na+ and can exhibit excellent electrochemical performance. Herein, the self-assembled hairball-like VS4 as anodes of SIBs exhibits high discharge capacity (660 and 589 mAh g-1 at 1 and 3 A g-1, respectively) and excellent rate property (about 100% retention at 10 and 20 A g-1 after 1000 cycles) at room temperature. Moreover, the VS4 can also exhibit 591 mAh g-1 at 1 A g-1 after 600 cycles at 0 °C. An unlike traditional mechanism of VS4 for Na+ storage was proposed according to the dates of ex situ characterization, cyclic voltammetry, and electrochemical kinetic analysis. The capacities of the final stabilization stage are provided by the reactions of reversible transformation between Na2S and S, which were considered the reaction mechanisms of Na-S batteries. This work can provide a basis for the synthesis and application of sulfur-rich compounds in fields of batteries, semiconductor devices, and catalysts.

Electrochemical performance of antimony/chlorine-incorporated nickel foam

In this paper, an Sb/Cl-incorporated nickel foam (NF) electrode material was grown on acid-pretreated NF by one-step chemical vapor deposition using SbCl₃ as the Sb source.