Rational design of few-layer MoSe2 confined within ZnSe-C hollow porous spheres for high-performance lithium-ion and sodium-ion batteries

Heterogeneous bimetallic selenides encapsulated within graphene aerogel as advanced anodes for sodium ion batteries

Metal selenides are promising anode candidates for sodium ion batteries (SIBs) because of their high theoretical capacity, low cost, and environmental friendship. However, the low rate capability at high current density due to its inherent low electrical conductivity and poor cycle stability caused by inevitable volume variations during cycling frustrate its practical applications. Herein, we have developed a simple metallic-organic frameworks (MOFs)-derived selenide strategy to synthesize a series of heterogeneous bimetallic selenides encapsulated within graphene aerogels (GA) as anodes for SIBs. The bimetallic selenides/GA composites have unique structural characteristics that can shorten the migration path for Na+/electrons and accommodate the volume variations via additional void space during cycling. The built-in electric fields induced at the heterointerfaces can greatly reduce the activation energy for rapid charge transfer kinetics and promote the diffusion of Na+/electrons. GA is also beneficial for accommodating the volume variations during cycling and improving conductivity. As an advanced anode for SIBs, the MoSe2-Cu1.82Se@GA with a special porous octahedron can deliver the highest capacity of 444.8 mAh/g at a high rate of 1 A/g even after 1000 cycles among the bimetallic selenides/GA composites.

Porous hybrid encapsulation enables high-rate lithium storage for a micron-sized SiO anode

Establishing a durable interfacial layer between an electrode and electrolyte to enable micron-sized silicon-based lithium-ion battery (LIB) anodes to achieve superior electrochemical performance is highly desired. Recent studies have shown that heterogeneous encapsulation with enhanced ion/electron transport is an effective strategy. However, the structural design of the existing hetero-coated interface lacks a reasonable ion/electron transport channel, resulting in high interfacial impedance. Herein, we designed a heterogenous MXene-mesoporous polypyrrole (mPPy) encapsulation layer onto micron-sized SiO particles. The MXene coating layer functions as a bridging interface that can build a strong chemical link to internal SiO via covalent bonding, thus reinforcing interfacial charge transfer rate. Meanwhile, it forms a dynamic connection with the outer mPPy through hydrogen bonding, which contributes to high interfacial Li+ concentration and ion/electron coupling transport rate. Accordingly, the as-prepared SiO@MXene@mPPy anode delivers a boosted specific capacity of 673.9 mA h g-1 at 2 A g-1 after 1000 cycles and high-rate capability of 777.4 mA h g-1 at 5 A g-1. Further, electrochemical kinetic analysis indicates that the MXene@mPPy coating layer shows a pseudocapacitance controlled Li storage mechanism, thereby displaying improved high-rate capability. This porous hybrid encapsulation strategy offers new possibilities for a micron-sized SiO anode to achieve an excellent performance.

Towards metal selenides: a promising anode for sodium-ion batteries

Metal selenides have garnered significant attention as promising anode materials for sodium-ion batteries, thanks to their high theoretical capacity, excellent conductivity, and natural abundance. However, their potential is hampered by disappointing capacity retention and unsatisfactory lifespan, primarily attributed to volume expansion and unwanted structural collapse resulting from the insertion and extraction of relatively large Na+ ions during the charge and discharge processes. This feature article provides a brief overview of our endeavors to address the challenges associated with metal selenide-based anode materials, aiming to achieve high-performance electrode materials for sodium-ion batteries. Our strategy encompasses nanostructure design, materials composite engineering, heteroatoms doping, and topography and interface engineering. Additionally, future research directions are also outlined.

A Hydrogel Electrolyte with High Adaptability over a Wide Temperature Range and Mechanical Stress for Long-Life Flexible Zinc-Ion Batteries

Flexible zinc-ion batteries have garnered significant attention in the realm of wearable technology. However, the instability of hydrogel electrolytes in a wide-temperature range and uncontrollable side reactions of the Zn electrode have become the main problems for practical applications. Herein, N,N-dimethylformamide (DMF) to design a binary solvent (H2O-DMF) is introduced and combined it with polyacrylamide (PAM) and ZnSO4 to synthesize a hydrogel electrolyte (denoted as PZD). The synergistic effect of DMF and PAM not only guides Zn2+ deposition on Zn(002) crystal plane and isolates H2O from the Zn anode, but also breaks the hydrogen bonding network between water to improve the wide-temperature range stability of hydrogel electrolytes. Consequently, the symmetric cell utilizing PZD can stably cycle over 5600 h at 0.5 mA cm- 2@0.5 mAh cm-2. Furthermore, the Zn//PZD//MnO2 full cell exhibits favorable wide-temperature range adaptability (for 16000 cycles at 3 A g-1 under 25 °C, 750 cycles with 98 mAh g-1 at 0.1 A g-1 under -20 °C) and outstanding mechanical properties (for lighting up the LEDs under conditions of pressure, bending, cutting, and puncture). This work proposes a useful modification for designing a high-performance hydrogel electrolyte, which provides a reference for investigating the practical flexible aqueous batteries.

Carbon Nanofibers-Based Anodes for Potassium-Ion Battery

In recent years, with the global warming getting worse and increasing demand for energy, countries around the world are trying to develop new energy storage technologies to solve this problem. Currently, potassium-ion batteries (PIBs) have attracted tremendous attention from researchers as low-cost and high-performance energy storage devices. However, due to the huge ionic radius of K+, PIBs face significant volume expansion during cycling, which can easily lead to the collapse of electrode structures. In addition, the poor diffusion kinetics of K+ seriously affect the electrochemical performance of the battery. Carbon nanofibers (CNFs)-based materials (including CNFs, metal/CNFs composites, chalcogenide/CNFs composites, and other CNFs-based materials) are widely used as PIBs electrode anode materials due to their three-dimensional conductive network, heteroatom doping and excellent mechanical properties. This review discusses in detail the research progress of CNFs-based materials in PIBs, including material preparation, structural design, and performance optimization. On this basis, this article explores the key issues faced by CNFs-based materials and future development directions, and proposes improvement suggestions for providing new ideas for the development of CNFs-based materials.

Transition Metal Selenide-Based Anodes for Advanced Sodium-Ion Batteries: Electronic Structure Manipulation and Heterojunction Construction Aspect

In recent years, sodium-ion batteries (SIBs) have gained a foothold in specific applications related to lithium-ion batteries, thanks to continuous breakthroughs and innovations in materials by researchers. Commercial graphite anodes suffer from small interlayer spacing (0.334 nm), limited specific capacity (200 mAh g-1), and low discharge voltage (<0.1 V), making them inefficient for high-performance operation in SIBs. Hence, the current research focus is on seeking negative electrode materials that are compatible with the operation of SIBs. Many studies have been reported on the modification of transition metal selenides as anodes in SIBs, mainly targeting the issue of poor cycling life attributed to the volume expansion of the material during sodium-ion extraction and insertion processes. However, the intrinsic electronic structure of transition metal selenides also influences electron transport and sodium-ion diffusion. Therefore, modulating their electronic structure can fundamentally improve the electron affinity of transition metal selenides, thereby enhancing their rate performance in SIBs. This work provides a comprehensive review of recent strategies focusing on the modulation of electronic structures and the construction of heterogeneous structures for transition metal selenides. These strategies effectively enhance their performance metrics as electrodes in SIBs, including fast charging, stability, and first-cycle coulombic efficiency, thereby facilitating the development of high-performance SIBs.

Reduced graphene oxide-wrapped ZnS-SnS2 heterojunction bimetallic hollow cubic boxes as high-magnification and long lifespan supercapacitor anode materials

Metal sulfides have attracted extensive attention due to their excellent electrochemical performance. However, issues such as poor conductivity and severe volume expansion during charge and discharge processes affect the applications of sulfides as electrode materials. Here, a combination of coprecipitation and high-temperature sulfidation methods are employed to synthesize a ZnS-SnS2 composite with a hollow cubic structure, which is further composited with reduced graphene oxide (RGO) to form ZnS-SnS2 hollow cubic boxes encapsulated in a conductive framework of reduced graphene oxide (RGO) (denoted as ZnS-SnS2@RGO) for electrode materials. The hollow structure effectively alleviates the pulverization of ZnS-SnS2@RGO caused by volume expansion during charge and discharge processes. The heterogeneous structure formed by ZnS and SnS2 effectively reduces the electron transfer resistance of the material. The use of RGO wrapping enhances the conductivity of the ZnS-SnS2 hollow cubic boxes, and RGO's dispersion effect on the ZnS-SnS2 cubes improves particle agglomeration, further mitigating volume expansion of the material. These results indicate the outstanding electrochemical performance of heterostructural ZnS-SnS2 hollow cubic electrodes encapsulated with reduced graphene oxide as a conductive framework. The fabrication process provides a novel approach for addressing volume expansion and poor conductivity issues in other pseudocapacitive materials.

Metal-Organic Framework-Based Materials for Advanced Sodium Storage: Development and Anticipation

As a pioneering battery technology, even though sodium-ion batteries (SIBs) are safe, non-flammable, and capable of exhibiting better temperature endurance performance than lithium-ion batteries (LIBs), because of lower energy density and larger ionic size, they are not amicable for large-scale applications. Generally, the electrochemical storage performance of a secondary battery can be improved by monitoring the composition and morphology of electrode materials. Because more is the intricacy of a nanostructured composite electrode material, more electrochemical storage applications would be expected. Despite the conventional methods suitable for practical production, the synthesis of metal-organic frameworks (MOFs) would offer enormous opportunities for next-generation battery applications by delicately systematizing the structure and composition at the molecular level to store sodium ions with larger sizes compared with lithium ions. Here, the review comprehensively discusses the progress of nanostructured MOFs and their derivatives applied as negative and positive electrode materials for effective sodium storage in SIBs. The commercialization goal has prompted the development of MOFs and their derivatives as electrode materials, before which the synthesis and mechanism for MOF-based SIB electrodes with improved sodium storage performance are systematically discussed. Finally, the existing challenges, possible perspectives, and future opportunities will be anticipated.

Novel hollow MoS2@C@Cu2S heterostructures for high zinc storage performance

Heterostructured materials have great potential as cathodes for zinc-ion batteries (ZIBs) because of their fast Zn2+ transport channels. Herein, hollow MoS2@C@Cu2S heterostructures are innovatively constructed using a template-engaged method. The carbon layer improves the electrical conductivity, provides a high in situ growth area, and effectively restricts volume expansion during the recycling process. MoS2 nanosheets are grown on the surfaces of hollow C@Cu2S nanocubes using the in situ template method, further expanding the specific surface area and exposing more active sites to enhance the electrical conductivity. As expected, an admirable reversible capacity of 197.2 mA h g-1 can be maintained after 1000 cycles with a coulombic efficiency of 91.1%. Therefore, we firmly believe that this work points the way forward for high-performance materials design and energy storage systems.

MOF-Derived Nitrogen-Doped Porous Carbon Polyhedrons/Carbon Nanotubes Nanocomposite for High-Performance Lithium-Sulfur Batteries

Nanocomposites that combine porous materials and a continuous conductive skeleton as a sulfur host can improve the performance of lithium-sulfur (Li-S) batteries. Herein, carbon nanotubes (CNTs) anchoring small-size (~40 nm) N-doped porous carbon polyhedrons (S-NCPs/CNTs) are designed and synthesized via annealing the precursor of zeolitic imidazolate framework-8 grown in situ on CNTs (ZIF-8/CNTs). In the nanocomposite, the S-NCPs serve as an efficient host for immobilizing polysulfides through physical adsorption and chemical bonding, while the interleaved CNT networks offer an efficient charge transport environment. Moreover, the S-NCP/CNT composite with great features of a large specific surface area, high pore volume, and short electronic/ion diffusion depth not only demonstrates a high trapping capacity for soluble lithium polysulfides but also offers an efficient charge/mass transport environment, and an effective buffering of volume changes during charge and discharge. As a result, the Li-S batteries based on a S/S-NCP/CNT cathode deliver a high initial capacity of 1213.8 mAh g-1 at a current rate of 0.2 C and a substantial capacity of 1114.2 mAh g-1 after 100 cycles, corresponding to a high-capacity retention of 91.7%. This approach provides a practical research direction for the design of MOF-derived carbon materials in the application of high-performance Li-S batteries.

Metal-Organic Assembly Strategy for the Synthesis of Layered Metal Chalcogenide Anodes for Na+ /K+ -Ion Batteries

Layered transition metal chalcogenides (MX, M=Mo, W, Sn, V; X=S, Se, Te) have large ion transport channels and high specific capacity, making them promising for large-sized Na⁺ /K⁺ energy-storage technologies. Nevertheless, slow reaction kinetics and huge volume expansion will induce an undesirable electrochemical performance. Numerous efforts have been devoted to designing MX anodes and enhancing their electrochemical performance. Based on the metal-organic assembly strategy, nanostructural engineering, combination with carbon materials, and component regulation can be easily realized, which effectively boost the performance of MX anodes. In this Review, we present a comprehensive overview on the synthesis of MX nanostructure using the metal-organic assembly strategy, which can realize the design of MX nanostructures, based on self-sacrificial templates, host@guest tailored templates, post-modified layer and derivative templates. The preparation routes and structure evolution are mainly discussed. Then, Mo-, W-, Sn-, V-based chalcogenides used for Na⁺ /K⁺ energy storage are reviewed, and the relationship between the structure and the electrochemical performance, as well as the energy storage mechanism are emphasized. In addition, existing challenges and future perspectives are also presented.

Progressive activation of porous vanadium nitride microspheres with intercalation-conversion reactions toward high performance over a wide temperature range for zinc-ion batteries

Rechargeable aqueous zinc-ion batteries have great promise for becoming next-generation storage systems, although the irreversible intercalation of Zn²⁺ and sluggish reaction kinetics impede their wide application. Therefore, it is urgent to develop highly reversible zinc-ion batteries. In this work, we modulate the morphology of vanadium nitride (VN) with different molar amounts of cetyltrimethylammonium bromide (CTAB). The optimal electrode has porous architecture and excellent electrical conductivity, which can alleviate volume expansion/contraction and allow for fast ion transmission during the Zn²⁺ storage process. Furthermore, the CTAB-modified VN cathode undergoes a phase transition that provides a better framework for vanadium oxide (VO_x). With the same mass of VN and VO_x, VN provides more active material after phase conversion due to the molar mass of the N atom being less than that of the O atom, thus increasing the capacity. As expected, the cathode displays an excellent electrochemical performance of 272 mAh g^-1 at 5 A g^-1, high cycling stability up to 7000 cycles, and excellent performance over a wide temperature range. This discovery creates new possibilities for the development of high-performance multivalent ion aqueous cathodes with rapid reaction mechanisms.

Hydrogen Bond-Enabled High-ICE Anode for Lithium-Ion Battery Using Carbonized Citric Acid-Coated Silicon Flake in PAA Binder

A silicon-based lithium-ion battery (LIB) anode is extensively studied because of silicon's abundance, high theoretical specific capacity (4200 mAh/g), and low operating potential versus lithium. Technical barriers to large-scale commercial applications include the low electrical conductivity and up to about 400% volume changes of silicon due to alloying with lithium. Maintaining the physical integrity of individual silicon particles and the anode structure is the top priority. We use strong hydrogen bonds between citric acid (CA) and silicon to firmly coat CA on silicon. Carbonized CA (CCA) enhances electrical conductivity of silicon. Polyacrylic acid (PAA) binder encapsulates silicon flakes by strong bonds formed by abundant COOH functional groups in PAA and on CCA. It results in excellent physical integrity of individual silicon particles and the whole anode. The silicon-based anode shows high initial coulombic efficiency, around 90%, and the capacity retention of 1479 mAh/g after 200 discharge-charge cycles at 1 A/g current. At 4 A/g, the capacity retention of 1053 mAh/g was achieved. A durable high-ICE silicon-based LIB anode capable of high discharge-charge current has been reported.

NiS2 nanoparticles by the NaCl-assisted less-liquid reaction system for the magnesium-ion battery cathode

Rechargeable magnesium batteries are expected to be the next generation of energy storage devices. Therefore, it is of great significance to develop low-cost and long-life magnesium (Mg) electrode materials. However, the traditional method of synthesizing electrode materials is complicated, and it is difficult to remove potentially dangerous impurities. In this study, without adding any additional solvent, the crystal water in the reactant provides a liquid environment directly for the reaction, such that the whole reaction could be carried out safely and efficiently in the less liquid reaction system. Furthermore, NiS₂ in the cotton-like form was synthesized under the spatial effect of NaCl solution in a confined space. The fabricated material was tightly connected and has abundant active sites, which promote the rapid transport of charge. This work provides a general strategy of preparation methods for metal sulfides and also points in a new direction for the improvement of electrochemical performance with less-liquid reaction systems without additional solvents.

Lithium Vanadium Oxide/Graphene Composite as a Promising Anode for Lithium-Ion Batteries

Lithium vanadium oxide (Li₃VO₄, LVO) is a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity (394 mAh g^-1) and safe working potential (0.5-1.0 V vs. Li⁺/Li). However, its electrical conductivity is low which leads to poor electrochemical performance. Graphene (GN) shows excellent electrical conductivity and high specific surface area, holding great promise in improving the electrochemical performance of electrode materials for LIBs. In this paper, LVO was prepared by different methods. SEM results showed the obtained LVO by sol-gel method possesses uniform nanoparticle morphology. Next, LVO/GN composite was synthesized by sol-gel method. The flexible GN could improve the distribution of LVO, forming a high conductive network. Thus, the LVO/GN composite showed outstanding cycling performance and rate performance. The LVO/GN composite can provide a high initial capacity of 350.2 mAh g^-1 at 0.5 C. After 200 cycles, the capacity of LVO/GN composite remains 86.8%. When the current density increased from 0.2 C to 2 C, the capacity of LVO/GN composite only reduced from 360.4 mAh g^-1 to 250.4 mAh g^-1, demonstrating an excellent performance rate.

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.

Sb-Doped metallic 1T-MoS2 nanosheets embedded in N-doped carbon as high-performance anode materials for half/full sodium/potassium-ion batteries

Metal 1T phase molybdenum disulfide (1T-MoS₂) is being actively considered as a promising anode due to its high conductivity, which can improve electron transfer. Herein, we elaborately designed stable Sb-doped metallic 1T phase molybdenum sulfide (1T-MoS₂-Sb) with a few-layered nanosheet structure via a simple calcination technique. The N-doping of the carbon and Sb-doping induce the formation of T-phase MoS₂, which not only effectively enhances the entire stability of the structure, but also improves its cycling performance and stability. When employed as an anode of sodium-ion batteries (SIBs), 1T-MoS₂-Sb exhibits a reversible capacity of 493 mA h g^-1 at 0.1 A g^-1 after 100 cycles and delivers prominent long-term performance (253 mA h g^-1 at 1 A g^-1 after 2200 cycles) along with decent rate capability. Paired with a Na₃V₂(PO₄)₃ cathode, it displays a superior capacity of 242 mA h g^-1 at 0.5 A g^-1 over 100 cycles, which is one of the best performances of a MoS₂-based full cell for SIBs. Employed as the anode for potassium-ion batteries (PIBs), it exhibits a satisfactory specific capacity of 343 mA h g^-1 at 0.1 A g^-1 after 100 cycles. This facile strategy will provide new insights for designing T-phase advanced anode materials for SIBs/PIBs.

Research progress on ZnSe and ZnTe anodes for rechargeable batteries

Transition-metal chalcogenides (TMCs) with tunable direct bandgaps and interlayer spacing are attractive for energy-related applications. Semiconducting zinc chalcogenides, especially their selenides (ZnSe) and tellurides (ZnTe), with enhanced conductivity, high theoretical capacity, low operation voltage and abundance, have appeared on the horizon and receive increasing interest in terms of electrochemical energy storage and conversion. Despite the existing typical obstruction owing to the large volume change, relatively low electrical conductivity and sluggish ion diffusion kinetics into the bulk phase, several effective strategies such as compositing, doping, nanostructuring, and electrode/cell design have exhibited promising applications. We herein provide a timely and systematic overview of recent research and significant advances regarding ZnSe, ZnTe and their hybrids/composites, covering synthesis to electrode design and to applications, especially in advanced Li/Na/K-ion batteries, as well as the reaction mechanisms thereof. It is hoped that the overview will shed new light on the development of ZnSe and ZnTe for next-generation rechargeable batteries.

Innovative Materials for Energy Storage and Conversion

The metal chalcogenides (MCs) for sodium-ion batteries (SIBs) have gained increasing attention owing to their low cost and high theoretical capacity. However, the poor electrochemical stability and slow kinetic behaviors hinder its practical application as anodes for SIBs. Hence, various strategies have been used to solve the above problems, such as dimensions reduction, composition formation, doping functionalization, morphology control, coating encapsulation, electrolyte modification, etc. In this work, the recent progress of MCs as electrodes for SIBs has been comprehensively reviewed. Moreover, the summarization of metal chalcogenides contains the synthesis methods, modification strategies and corresponding basic reaction mechanisms of MCs with layered and non-layered structures. Finally, the challenges, potential solutions and future prospects of metal chalcogenides as SIBs anode materials are also proposed.

Vanadium nitride@carbon nanofiber composite: Synthesis, cascade enzyme mimics and its sensitive and selective colorimetric sensing of superoxide anion

Nanozymes featuring with favorable activity, good stability and easy scale-up production, are promising to replace natural enzymes for various applications. However, it remains a challenge to explore the cascade reactions of multi-enzyme mimics, aiming at synergistic catalysis for various applications. Herein, vanadium nitride nanoparticles deposited on carbon nanofibers (VN@CNFs) composite was facilely prepared by typical electrospinning route with subsequently ammonia reduction process. The nanocomposite showed excellent peroxidase (POD)-like and superoxide dismutase (SOD)-like activities. Additionally, their catalytic mechanisms were systematically researched. Coupling of SOD-like with POD-like as cascade enzyme, a selective and sensitive colorimetric detection of superoxide anion (O₂^•-) was explored, which has two linear parts, 0.05-30 μM and 30-250 μM O₂^•- with the LOD of 0.0167 μM (S/N = 3). The as-proposed method was applicable to practical samples detection with satisfactory accuracy and recovery. Therefore, the VN@CNFs composite shows great prospect in biosensing, superoxide anion removal and biocatalysis.

Structure Engineering of BiSbSx Nanocrystals Embedded within Sulfurized Polyacrylonitrile Fibers for High Performance of Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are regarded as promising candidates in next-generation energy storage technology; however, the electrode materials in PIBs are usually restricted by the shortcomings of large volume expansion and poor cycling stability stemming from a high resistance towards diffusion and insertion of large-sized K ions. In this study, BiSbS_x nanocrystals are rationally integrated with sulfurized polyacrylonitrile (SPAN) fibres through electrospinning technology with an annealing process. Such a unique structure, in which BiSbS_x nanocrystals are embedded inside the SPAN fibre, affords multiple binding sites and a short diffusion length for K⁺ to realize fast kinetics. In addition, the molecular structure of SPAN features robust chemical interactions for stationary diffluent discharge products. Thus, the electrode demonstrates a superior potassium storage performance with an excellent reversible capacity of 790 mAh g^-1 (at 0.1 A g^-1 after 50 cycles) and 472 mAh g^-1 (at 1 A g^-1 after 2000 cycles). It's one of the best performances for metal dichalcogenides anodes for PIBs to date. The unusual performance of the BiSbS_x @SPAN composite is attributed to the synergistic effects of the judicious nanostructure engineering of BiSbS_x nanocrystals as well as the chemical interaction and confinement of SPAN fibers.

Enhanced Li-Ion Rate Capability and Stable Efficiency Enabled by MoSe2 Nanosheets in Polymer-Derived Silicon Oxycarbide Fiber Electrodes

Transition metal dichalcogenides (TMDs) such as MoSe2 have continued to generate interest in the engineering community because of their unique layered morphology-the strong in-plane chemical bonding between transition metal atoms sandwiched between two chalcogen atoms and the weak physical attraction between adjacent TMD layers provides them with not only chemical versatility but also a range of electronic, optical, and chemical properties that can be unlocked upon exfoliation into individual TMD layers. Such a layered morphology is particularly suitable for ion intercalation as well as for conversion chemistry with alkali metal ions for electrochemical energy storage applications. Nonetheless, host of issues including fast capacity decay arising due to volume changes and from TMD's degradation reaction with electrolyte at low discharge potentials have restricted use in commercial batteries. One approach to overcome barriers associated with TMDs' chemical stability functionalization of TMD surfaces by chemically robust precursor-derived ceramics or PDC materials, such as silicon oxycarbide (SiOC). SiOC-functionalized TMDs have shown to curb capacity degradation in TMD and improve long term cycling as Li-ion battery (LIBs) electrodes. Herein, we report synthesis of such a composite in which MoSe2 nanosheets are in SiOC matrix in a self-standing fiber mat configuration. This was achieved via electrospinning of TMD nanosheets suspended in pre-ceramic polymer followed by high temperature pyrolysis. Morphology and chemical composition of synthesized material was established by use of electron microscopy and spectroscopic technique. When tested as LIB electrode, the SiOC/MoSe2 fiber mats showed improved cycling stability over neat MoSe2 and neat SiOC electrodes. The freestanding composite electrode delivered a high charge capacity of 586 mAh g-1electrode with an initial coulombic efficiency of 58%. The composite electrode also showed good cycling stability over SiOC fiber mat electrode for over 100 cycles.

Facile fabrication of WS2 nanocrystals confined in chlorella-derived N, P co-doped bio-carbon for sodium-ion batteries with ultra-long lifespan

Sodium-ion batteries (SIBs) have been regarded as a promising substitute for lithium-ion batteries but there are still formidable challenges in developing an anode material with adequate lifespan and outstanding rate performance. Transition metal dichalcogenides (TMDs) are promising anode materials for SIBs due to their high theoretical capacities. However, their severe volume expansions and low electronic conductivity impede their practical developments. In addition, the synthesis of energy storage materials from waste biomass has aroused extensive attention. Herein, we synthesize WS₂ nanocrystals embedded in N and P co-doped biochar via a facile bio-sorption followed by sulphurization, employing waste chlorella as the adsorbent and bio-reactor. The WS₂ nanocrystals are beneficial for storing more sodium ions and expediting the transportation of sodium ions, thus improving the capacity and reaction kinetics. Chlorella acts as a reactor and not only inhibits the stacking of WS₂ nanocrystals during the synthesis process but also alleviates the mechanical pressure of composite during the charge/discharge process. As a result, the WS₂/NPC-2 electrode delivers a high specific capacity (436 mA h g^-1 at 0.1 A g^-1) and superior rate performance of 311 mA h g^-1 at 3 A g^-1 for SIBs. It also exhibits excellent stability even up to 6000 cycles at 5 A g^-1, which is one of the optimal long-cycle properties reported for WS₂-based materials to date.

Fabrication of ZnSe/C Hollow Polyhedrons for Lithium Storage

ZnSe has got extensive attention for high-performance LIBs anode due to its remarkable theoretical capacity and environmental friendliness. Nevertheless, the large volume variation for the ZnSe in the discharge/charge processes brings about rapid capacity fading and poor rate performance. Herein, ZnSe/C hollow polyhedrons are successfully synthesized by selenization of zeolitic imidazolate framework-8 (ZIF-8) with resorcinol-formaldehyde (RF) coating. The protection of C layer derived from RF coating layer and Ostwald ripening during the process of selenization play important roles in promoting formation of ZnSe/C hollow polyhedrons. The ZnSe/C hollow polyhedrons exhibit good rate performance and long-term cycle stability (345 mAh g^-1 up to 1000 cycles at 1 A g^-1 ) for lithium ion batteries (LIBs) anode. The improved electrochemical performance is benefit from the unique ZnSe/C hollow structure, in which the hollow structure can effectively avoid terrible volume expansion, and the thin ZnSe/C shell can not only provide adequate diffusion paths of lithium ions and but also enhance the electronic conductivity.

Metal-organic framework based electrode materials for lithium-ion batteries: a review

Metal–organic frameworks (MOFs) with efficient surface and structural properties have risen as a distinctive class of porous materials through the last few decades, which has enabled MOFs to gain attention in a wide range of applications like drug delivery, gas separation and storage, catalysis and sensors. Likewise, they have also emerged as efficient active materials in energy storage devices owing to their remarkable conducting properties. Metal–organic frameworks (MOFs) have garnered great interest in high-energy-density rechargeable batteries and super-capacitors. Herein the study presents their expanding diversity, structures and chemical compositions which can be tuned at the molecular level. It also aims to evaluate their inherently porous framework and how it facilitates electronic and ionic transportation through the charging and discharging cycles of lithium-ion batteries. In this review we have summarized the various synthesis paths to achieve a particular metal–organic framework. This study focuses mainly on the implementation of metal–organic frameworks as efficient anode and cathode materials for lithium-ion batteries (LIBs) with an evaluation of their influence on cyclic stability and discharge capacity. For this purpose, a brief assessment is made of recent developments in metal–organic frameworks as anode or cathode materials for lithium-ion batteries which would provide enlightenment in optimizing the reaction conditions for designing a MOF structure for the battery community and electrochemical energy storage applications.

In this review article, a comprehensive insight is given into current progress of electrochemical evaluation of MOFs based material as efficient anode and cathode materials for LIBs.

Rational design of MoSe2 nanosheet-coated MOF-derived N-doped porous carbon polyhedron for potassium storage

For potassium-ion battery (PIB), it remains a huge challenge to develop an appropriate anode material to compensate the large radius of K⁺. MoSe₂ shows great potential for efficient K⁺ insertion/extraction due to its unique lamellar structures with an interlayer spacing of 6.46 Å. However, pure MoSe₂ has low electronic conductivity and agglomerates during long-term cycling. In the present work, MoSe₂ nanosheets were fabricated on the N-doped porous carbon polyhedron (NPCP). The obtained product was designated as NPCP@MoSe₂ and functioned as anode materials for PIBs. NPCP@MoSe₂ displayed a promising reversible capacity (325 mAh/g at 100 mA/g after 80 cycles), long-term cycling performance (128 mAh/g at 500 mA/g after 800 cycles), and superior rate property at 5000 mA/g. The enhanced electrochemical performance of NPCP@MoSe₂ could be attributed to the rational design of hybrid structures. Notably, the hollow NPCP provide a large contact area for the interactions among the electrolytes and electro-active materials as well as partly buffer the volume expansion. The synergistic effects between MoSe₂ and NPCP could mitigate the agglomeration of MoSe₂ nanosheets. Besides, the uniformly doping N elements enhanced the conductivity of the carbon matrix, and the N-group also provided potential binding active sites for K-ion accommodation. This work paves the ideas for the design of novel anode materials with high specific capacity, good cycling stability and outstanding rate capability for PIBs.

Nitrogen-doped carbon encapsulated zinc vanadate polyhedron engineered from a metal-organic framework as a stable anode for alkali ion batteries

In this work, we fabricated vanadium/zinc metal-organic frameworks (V/Zn-MOFs) derived from self-assembled metal organic frameworks, to further disperse ultrasmall Zn₂VO₄ nanoparticles and encapsulate them in a nitrogen-doped nanocarbon network (ZVO/NC) under in situ pyrolysis. When employed as an anode for lithium-ion batteries, ZVO/NC delivers a high reversible capacity (807 mAh g^-1 at 0.5 A g^-1) and excellent rate performance (372 mAh g^-1 at 8.0 A g^-1). Meanwhile, when used in sodium-ion batteries, it exhibits long-term cycling stability (7000 cycles with 145 mAh g^-1 at 2.0 A g^-1). Additionally, when employed in potassium-ion batteries, it also shows outstanding electrochemical performance with reversible capacities of 264 mAh g^-1 at 0.1 A g^-1 and 140 mAh g^-1 at 0.5 A g^-1 for 1000 cycles. The mechanism by which the pseudocapacitive behaviour of ZVO/NC enhances battery performance under a suitable electrolyte was probed, which offers useful enlightenment for the potential development of anodes of alkali-ion batteries. The performance of Zn₂VO₄ as an anode for SIBs/PIBs was investigated for the first time. This work provides a new horizon in the design ZVO/NC as a promising anode material owing to the intrinsically synergic effects of mixed metal species and the multiple valence states of V.

Co-construction of sulfur vacancies and carbon confinement in V5S8/CNFs to induce an ultra-stable performance for half/full sodium-ion and potassium-ion batteries

The construction of anode materials for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) with a high energy and a long lifespan is significant and still challenging. Here, sulfur-defective vanadium sulfide/carbon fiber composites (D-V5S8/CNFs) are designed and fabricated by a facile electrospinning method, followed by sulfuration treatment. The unique architecture, in which V5S8 nanoparticles are confined inside the carbon fiber, provides a short-range channel and abundant adsorption sites for ion storage. Moreover, enlarged interlayer spacings could also alleviate the volume changes, and offer small vdW interactions and ionic diffusion resistance to store more Na and K ions reversibly and simultaneously. The DFT calculations further demonstrate that sulfur defects can effectively facilitate the adsorption behavior of Na+ and K+ and offer low energy barriers for ion intercalation. Taking advantage of the functional integration of these merits, the D-V5S8/CNF anode exhibits excellent storage performance and long-term cycling stability. It reveals a high capacity of 462 mA h g-1 at a current density of 0.2 A g-1 in SIBs, while it is 350 mA h g-1 at 0.1 A g-1 in PIBs, as well as admirable long-term cycling characteristics (190 mA h g-1/17 000 cycles/5 A g-1 for SIBs and 165 mA h g-1/3000 cycles/1 A g-1 for PIBs). Practically, full SIBs upon pairing with a Na3V2(PO4)3 cathode also exhibit superior performance.

Dual carbon decorated germanium-carbon composite as a stable anode for sodium/potassium-ion batteries

In the present work, we introduce a dual carbon accommodated structure in which germanium nanoparticles are encapsulated into an ordered mesoporous carbon matrix (Ge-CMK) and further coated with an amorphous carbon layer (Ge@C-CMK) through a nano-casting route followed by chemical vapor deposition (CVD) treatment. In the resultant Ge@C-CMK composite, the unique lane-like pore structure that cooperates with the amorphous carbon surface can not only mitigate the volume expansion of germanium particles, but also improve the electrical conductivity of germanium as well as facilitate Na⁺/K⁺ diffusion. When employed as the anode of sodium-ion batteries, the Ge@C-CMK electrode exhibits stable capacity as well as long-term cycling stability (a stable capacity of 176 mAh g^-1 at 1 A g^-1 after 5000 cycles). Furthermore, it also delivers a reversible capacity when used as the anode of potassium-ion batteries. This demonstrates that the Ge@C-CMK electrode possesses promising application potential as an alternative anode in sodium and potassium ion storage applications.

Metal–organic framework-engaged synthesis of core–shell MoO2/ZnSe@N-C nanorods as anodes in high-performance lithium-ion batteries

A MoO₂/ZnSe@N-C nanorod was prepared through novel carbonization and selenization methods, shedding light on the design and application of metal selenides.

Nitrogen-doped carbon encapsulated hollow ZnSe/CoSe2 nanospheres as high performance anodes for lithium-ion batteries

Hierarchical nitrogen-doped carbon encapsulated hollow ZnSe/CoSe2 (ZnSe/CoSe2@N-C) nanospheres are fabricated by a convenient solvothermal and selenization approach, followed by a carbonization process. The as-obtained ZnSe/CoSe2@N-C possesses a multilevel nanoscale architecture composed of a thin carbon shell with a size of around 12 nm and hollow selenide nanoparticles as the core with tiny rough grains and rich voids as the subunits. The robust carbon protective shell and synergistic effect between double metal ions boost the electron and ion transportation as well as promote effective extraction and insertion of lithium ions. Hollow ZnSe/CoSe2@N-C spheres show high reversible capacity with 1153 mA h g-1 remaining over 100 cycles at 100 mA g-1. In particular, the hollow ZnSe/CoSe2@N-C spheres show an outstanding cycling stability at a high rate of 2000 mA g-1 with the reversible capacity of up to 966 mA h g-1 remaining after 500 cycles. As an advanced anode, ZnSe/CoSe2@N-C composite shows remarkable cycling stability and exceptional rate capability in the field of energy storage technologies.

Willow-Leaf-Like ZnSe@N-Doped Carbon Nanoarchitecture as a Stable and High-Performance Anode Material for Sodium-Ion and Potassium-Ion Batteries

ZnSe is regarded as a promising anode material for energy storage due to its high theoretical capacity and environment friendliness. Nevertheless, it is still a significant challenge to obtain superior electrode materials with stable performance owing to the serious volume change and aggregation upon cycling. Herein, a willow-leaf-like nitrogen-doped carbon-coated ZnSe (ZnSe@NC) composite synthesized through facile solvothermal and subsequent selenization process is beneficial to expose more active sites and facilitate the fast electron/ion transmission. These merits significantly enhance the electrochemical performances of ZnSe@NC for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). The obtained ZnSe@NC exhibits outstanding rate performance (440.3 mAh g^-1 at 0.1 A g^-1 and 144.4 mAh g^-1 at 10 A g^-1 ) and ultralong cycle stability (242.2 mAh g^-1 at 8.0 A g^-1 even after 3200 cycles) for SIBs. It is noted that 106.5 mAh g^-1 can be retained after 550 cycles and 71.4 mAh g^-1 is still remained after 1500 cycles at 200 mA g^-1 when applied as anode for PIBs, indicating good cycle stability of the electrode. The possible electrochemical mechanism and the ionic diffusion kinetics of the ZnSe@NC are investigated using ex situ X-ray diffraction, high-resolution transmission electron microscopy, and a series of electrochemical analyses.

Synthesis of the Se-HPCF composite via a liquid-solution route and its stable cycling performance in Li-Se batteries

In pursuit of a one-dimensional (1D) porous carbon framework to restrain selenium for advanced lithium-selenium batteries, the Se-hierarchical porous carbon fiber composite (Se-HPCF) is synthesized via a liquid-solution route followed by calcination treatment. The unique architecture of the HPCF, which exhibits a large surface area and high pore volume, is fabricated using sodium lignosulfonate (LN) as a green pore-forming agent via electrospinning. As a cathode material for Li-Se batteries, the Se-HPCF composite exhibits superior electrochemical performance. A reversible capacity of 533 mA h g-1 is maintained at a rate of 0.2C after 50 cycles. In addition, the Se-HPCF composite delivers high rate performance with a high specific capacity of 351 mA h g-1 at 5C. The enhanced capacity retention and rate performance of Se-HPCF is generated by the 1D structure characteristics, and the liquid phase melting diffusion method could be applied to produce other related materials.

Fabrication of Magnetic Superstructure NiFe2O4@MOF-74 and Its Derivative for Electrocatalytic Hydrogen Evolution with AC Magnetic Field

As an ideal hydrogen production route, electrolyzed water still faces the challenges of high cost of noble-metal electrocatalysts and low performance of non-noble-metal catalysts in scalable applications. Recently, introduction of external fields (such as magnetic fields, light fields, etc.) to improve the electrocatalytic water splitting performance of non-noble-metal catalysts has attracted great attention due to their simplicity. Here, a simple method for preparing magnetic superstructure (NiFe₂O₄@MOF-74) is described, and the hydrogen evolution reaction (HER) behavior of its carbonized derivative, a ferromagnetic superstructure, is revealed in a wide range of applied voltage under an AC magnetic field. The overpotential (@10 mA cm^-2) required for the HER of the obtained ferromagnetic superstructure in 1 M KOH was reduced by 31 mV (7.7%) when a much small AC magnetic field (only 2.3 mT) is applied. Surprisingly, the promotion effect of the AC magnetic field is not monotonically increasing with the increase of the applied voltage or the strength of AC magnetic field, but increasing first, then weakening. This unusual behavior is believed to be mainly caused by the enhanced induced electromotive force and the additional energy by the applied AC magnetic field. This discovery provides a new idea for adjusting the performance of electrocatalytic reactions.

Tailor-Made Gives the Best Fits: Superior Na/K-Ion Storage Performance in Exclusively Confined Red Phosphorus System

As the most promising anodic candidate for alkali ion batteries, red phosphorus (P) still faces big challenges, such as the poor rate and cycling performance, which are caused by the insulative nature and the large volume change throughout the alloy/dealloy process. To ameliorate above issues, the traditional way is confining P into the carbon host. However, investigations on maximizing P utilization are inadequate; in other words, how to achieve entire confinement with a high loading amount is still a problem. Additionally, the application of P in potassium-ion batteries (PIBs) is in its infant stage, and the corresponding potassiation product is controversial. Herein, a nitrogen-doped stripped-graphene CNT (N-SGCNT) as carbon framework is prepared to exclusively confine ultrafine P to construct P@N-SGCNT composites. Benefitting from the in situ cross-linked structure, N-SGCNT loaded with 41.2 wt % P (P₂@N-SGCNT) shows outstanding Na⁺/K⁺ storage performance. For instance, P₂@N-SGCNT exhibits high reversible capacities of 2480 mAh g^-1 for sodium-ion batteries (SIBs) and 762 mAh g^-1 for PIBs, excellent rate capabilities of 1770 mAh g^-1 for SIBs and 354 mAh g^-1 for PIBs at 2.0 A g^-1, and long cycling stability (a capacity of 1936 mAh g^-1 after 2000 cycles for SIBs and 319 mAh g^-1 after 1000 cycles for PIBs). Furthermore, due to this exclusively confined P structure, the K⁺ storage mechanism with the end product of K₄P₃ has been identified by experimental and theoretical results.

Hollow N-doped carbon nanofibers provide superior potassium-storage performance

Potassium-ion batteries (PIBs) are attractive as an alternative to lithium-ion batteries in emerging energy storage devices. However, a big challenge is to design advanced anode materials with fast charge/discharge and extended lifespan. Herein, a series of hollow N-doped carbon nanofibers (HNCNFs) were derived from polyaniline. As an anode for PIBs, HNCNFs exhibit an ultra-high rate capability of 139.7 mA h g^-1 at 30 A g^-1 and an ultra-long cycling life of 188.4 mA h g^-1 at 1 A g^-1 after 4000 cycles. These prominent performances can be ascribed to: (i) the enlarged interlayer spacing, which accommodates more K⁺ and larger (de)potassiation strain without fracture; (ii) the interconnected hollow nanofibers, which shorten ion diffusion distance and provide enough space to buffer volume change and sufficient electrolyte diffusion paths to ensure enhanced reaction efficiency of active materials; and (iii) high-content pyridinic/pyrrolic N-doping, which improves electrical conductivity, creates more active sites and enhances surface pseudocapacitive behavior, benefiting rapid K⁺ diffusion. This study provides a facile and cost-effective strategy to fabricate high-performance PIB anode materials on a large scale.

Cation-exchange construction of ZnSe/Sb2Se3 hollow microspheres coated by nitrogen-doped carbon with enhanced sodium ion storage capability

Recently, anode materials with synergistic sodium storage mechanisms of conversion combined with alloying reactions for sodium ion batteries (SIBs) have received widespread attention due to their high theoretical capacities. In this work, through reacting with an appropriate concentration of Sb³⁺ ions and a simple carbonization process, hollow ZnSe/Sb₂Se₃ microspheres encapsulated in nitrogen-doped carbon (ZnSe/Sb₂Se₃@NC) are progressively synthesized based on a cation-exchange reaction, using polydopamine-coated ZnSe (ZnSe@PDA) microspheres as the precursor. Benefiting from the synergistic effects between the unique structure and composition characteristics, when serving as an anode material for SIBs, they result in higher sodium diffusion coefficients (8.7 × 10^-13-3.98 × 10^-9 cm² s^-1) and ultrafast pseudocapacitive sodium storage capability. Compared with ZnSe@NC and Sb₂Se₃@NCs exhibit, ZnSe/Sb₂Se₃@NC exhibits more stable capacity (438 mA h g^-1 at a current of 0.5 A g^-1 after 120 cycles) and superior rate performance (316 mA h g^-1 at 10.0 A g^-1). Our work provides a convenient method to construct high performance anodes with tunable composition and structure for energy storage.

Mo-Doped SnO2 Nanoparticles Embedded in Ultrathin Graphite Nanosheets as a High-Reversible-Capacity, Superior-Rate, and Long-Cycle-Life Anode Material for Lithium-Ion Batteries

A new ternary Mo-SnO₂-graphite composite has been constructed via hydrothermal and ball milling. The Mo/SnO₂ hybrids were homogeneously dispersed in graphite nanosheets. In the Mo-SnO₂-graphite, Mo can inhibit the Sn nanoparticle aggregation, enhance the reversible conversion reaction in lithiation, and improve the electrochemical performance. Consequently, the Mo-SnO₂-graphite composite contributes a high capacity of 1317.4 mAh g^-1 at 0.2 A g^-1 after 200 cycles, remarkable rate property of 514.0 mAh g^-1 at 5 A g^-1, and long-term cyclic stabilization of 759.0 mAh g^-1 after 950 cycles at 1.0 A g^-1. With outstanding electrochemical performance and facial synthesis, the ternary Mo-SnO₂-graphite is a hopeful anode material for lithium-ion batteries (LIBs).

Bimetallic organic framework derivation of three-dimensional and heterogeneous metal selenides/carbon composites as advanced anodes for lithium-ion batteries

Heterogeneous structures have been attracting increasing attention in energy storage and conversion applications due to the phase interface and synergistic effect of multiple components. Herein, bimetal organic framework analogues were introduced to construct a Zn/Co bimetallic selenide heterostructure within a 3D-porous N-doped carbon matrix by a NaCl template-assisted lyophilization and annealing process. The cross-linked 3D network can enhance the transport kinetics for both lithium ions and electrons. The stress resulting from the cycling process can be released by interconnected channels in the composite. ZnSe and CoSe₂ experience electrochemical reactions at different potentials, which can buffer volume changes mutually to effectively increase structural stability. Meanwhile, abundant active sites due to the heterostructure enhance pseudocapacitive performance and reaction kinetics, resulting in high specific capacity and good rate performance. As anode materials for lithium-ion batteries, the three-dimensional ZnSe/CoSe₂-C composite exhibits a high reversible capacity of 700 mA h g^-1 after 500 cycles at 1 A g^-1.

Facile fabrication of a vanadium nitride/carbon fiber composite for half/full sodium-ion and potassium-ion batteries with long-term cycling performance

Vanadium-based composite anodes have been designed for applications in alkali metal ion batteries, including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). However, the problems of inferior long-term cycling stability caused by the large volume change and dissolution of vanadium-based active materials during cycles and slow diffusion for large radii of Na⁺ and K⁺ still limit their underlying capability and need to be addressed. In the present work, we initially designed and fabricated a vanadium nitride/carbon fiber (VN/CNF) composite via a facile electrospinning method followed by the ammonization process. The obtained VN/CNF composite anode exhibited excellent half/full sodium and potassium storage performance. When used as an anode material for SIBs, it delivered a high capacity of 403 mA h g^-1 at 0.1 A g^-1 after 100 cycles and as large as 237 mA h g^-1 at 2 A g^-1 even after 4000 cycles with negligible capacity fading. More importantly, the VN/CNFs//Na₃V₂(PO₄)₃ full cell by coupling the VN/CNF composite anode with the Na₃V₂(PO₄)₃ (NVP) cathode also exhibited a desirable capacity of 257 mA h g^-1 at 500 mA g^-1 after 50 cycles. Besides, when further evaluated as an anode for PIBs, the VN/CNF composite anode achieved a large capacity of 266 mA h g^-1 after 200 cycles at 0.1 A g^-1 and maintained a stable capacity of 152 mA h g^-1 at 1 A g^-1 even after 1000 cycles, showing significant long-term cycling stability. This is one of the best performances of vanadium-based anode materials for SIBs and PIBs reported so far.

Enhanced sodium storage kinetics by volume regulation and surface engineering via rationally designed hierarchical porous FeP@C/rGO

Transition metal phosphides, such as iron phosphide (FeP), have been considered as promising anode candidates for high-performance sodium ion batteries (SIBs) owing to their high theoretical capacity. However, the development of FeP is limited by large volume change, low electrical conductivity and sluggish kinetics with sodium ions. Moreover, the sodium storage kinetics and dynamics behavior in FeP are still unclear. Herein, improved sodium storage ability of FeP is achieved by volume regulation and surface engineering via a rationally designed hierarchical porous FeP@C/rGO nanocomposite. This FeP@C/rGO nanocomposite exhibits excellent rate capability and long cycle life as the anode of SIBs. Specifically, the FeP@C/rGO nanocomposite delivers high specific capacities of 635.7 and 343.1 mA h g-1 at 20 and 2000 mA g-1, respectively, and stable cycling with 88.2% capacity retention after 1000 cycles. The kinetics and dynamics studies demonstrate that the superior performance is attributed to the rationally designed hierarchical porous FeP@C/rGO with a high capacitive contribution of 93.9% (at 2 mV s-1) and a small volume expansion of only 54.9% by in situ transmission electron microscopy (TEM) measurement. This work provides valuable insights into understanding the phase evolution of FeP during the sodiation/desodiation process for designing high-performance SIBs.

Nanostructured metal chalcogenides confined in hollow structures for promoting energy storage

The engineering of progressive nanostructures with subtle construction and abundant active sites is a key factor for the advance of highly efficient energy storage devices. Nanostructured metal chalcogenides confined in hollow structures possess abundant electroactive sites, more ions and electron pathways, and high local conductivity, as well as large interior free space in a quasi-closed structure, thus showing promising prospects for boosting energy-related applications. This review focuses on the most recent progress in the creation of diverse confined hollow metal chalcogenides (CHMCs), and their electrochemical applications. Particularly, by highlighting certain typical examples from these studies, a deep understanding of the formation mechanism of confined hollow structures and the decisive role of microstructure engineering in related performances are discussed and analyzed, aiming at prompting the nanoscale engineering and conceptual design of some advanced confined metal chalcogenide nanostructures. This will appeal to not only the chemistry-, energy-, and materials-related fields, but also environmental protection and nanotechnology, thus opening up new opportunities for applications of CHMCs in various fields, such as catalysis, adsorption and separation, and energy conversion and storage.