Hierarchical Nanospheres Constructed by Ultrathin MoS2 Nanosheets Braced on Nitrogen-Doped Carbon Polyhedra for Efficient Lithium and Sodium Storage

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.

Cl- and Al-Doped Argyrodite Solid Electrolyte Li6PS5Cl for All-Solid-State Lithium Batteries with Improved Ionic Conductivity

Argyrodite solid electrolytes such as lithium phosphorus sulfur chloride (Li₆PS₅Cl) have recently attracted great attention due to their excellent lithium-ion transport properties, which are applicable to all-solid-state lithium batteries. In this study, we report the improved ionic conductivity of an argyrodite solid electrolyte, Li₆PS₅Cl, in all-solid-state lithium batteries via the co-doping of chlorine (Cl) and aluminum (Al) elements. Electrochemical analysis was conducted on the doped argyrodite structure of Li₆PS₅Cl, which revealed that the substitution of cations and anions greatly improved the ionic conductivity of solid electrolytes. The ionic conductivity of the Cl- and Al-doped Li₆PS₅Cl (Li_5.4Al_0.1PS_4.7Cl_1.3) electrolyte was 7.29 × 10^-3 S cm^-1 at room temperature, which is 4.7 times higher than that of Li₆PS₅Cl. The Arrhenius plot of the Li_5.4Al_0.1PS_4.7Cl_1.3 electrolyte further elucidated its low activation energy at 0.09 eV.

Synthesis of Nanostructured Bismuth Sulfide with Controllable Morphology for Advanced Lithium/Sodium-Ion Storage

Rational design of electrode materials with an excellent structure and morphology is crucial for improving electrochemical properties. Herein, various unique nanostructured Bi₂S₃ materials with controllable morphology were obtained through a simple and efficient oil bath reaction strategy. Bi₂S₃ with different morphologies can be obtained by regulating the polarity of solvent, and the lattice spacing can also be adjusted. The Bi₂S₃ nanomaterials obtained with ethanol as solvent (BS-3) show a three-dimensional nanoflower-like structure assembled with porous layers. The unique structure facilitates the transport of ions and accommodates the volume variation of Bi₂S₃ during energy storage. Consequently, BS-3 nanoflowers exhibited superior cycling stability and excellent high-rate capability for lithium storage (maintained a high capacity of 923.8 mA h g^-1 after 950 cycles at 1.0 A g^-1) and excellent sodium storage. We provide guidance for precise synthesis and energy storage application of Bi₂S₃ nanomaterials.

Dual-Type Carbon Confinement Strategy: Improving the Stability of CoTe2 Nanocrystals for Sodium-Ion Batteries with a Long Lifespan

Sodium-ion batteries have great potential to become large-scale energy storage devices due to their abundant and low-cost resources. However, the lack of anode and cathode materials with both high energy density and long-term cycling performance significantly affects their commercial applications. In this work, uniform CoTe₂ nanoparticles are generated from the tellurization of Co nanoparticles, which were coated with polyvinylpyrrolidone in a three-dimensional (3D) porous carbon matrix (CoTe₂@3DPNC). Finally, a dual-type carbon confinement structure is formed after tellurization during which citric acid is adopted as the source of the inner carbon scaffold. The hierarchical carbon matrix not only builds a robust and fast ion/electronic conductive 3D architecture but also mitigates the volume expansion and aggregation of CoTe₂ during sodium insertion/extraction. Remarkably, the CoTe₂@3DPNC electrode displays a high reversible capacity (216.5 mAh g^-1/627.9 mAh cm^-3 at 0.2 A g^-1 after 200 cycles) and outstanding long-term cycling performance (118.1 mAh g^-1/342.5 mAh cm^-3 even at 5.0 A g^-1 after 2500 cycles). Kinetics tests and capacitance calculations clearly reveal a battery-capacitive dual-model Na-storage mechanism. Furthermore, ex situ XRD/SEM/TEM demonstrate superior stability during sodium insertion/extraction. This work provides a valuable strategy for the rational structural design of long-life electrodes for advanced rechargeable batteries.

Coal-Derived Graphene/MoS2 Heterostructure Electrodes for Li-Ion Batteries: Experiment and Simulation Study

A novel coal-derived graphene-intercalated MoS₂ heterostructure was prepared with a facile in situ hydrothermal approach followed by high-temperature calcination. XRD, FE-SEM, HR-TEM, HR-Raman, and TOC analytical instruments, combined with first-principles simulations, were employed to explore the structural and electrochemical properties of this heterostructure for use as an electrode material. The XRD measurements and simulations confirmed the formation of the MoS₂/graphene (MoS₂-G) heterostructure. The microstructure analysis indicated that a well-defined 3D flower-like structure with tunable interlayer distances was created in the MoS₂ layer. The novel MoS₂-09% G anode exhibits a remarkable initial discharge capacity of ∼929 mAh/g due to its interlayer expansion from the intercalation of graphene between the MoS₂ layers. This anode maintains a capacity of ∼813 mAh/g with a Coulombic efficiency (CE) of ∼99% after 150 cycles at a constant current density of 100 mA/g. This anode also delivers a high-rate capability of ∼579 mAh/g at a current density of 2000 mA/g, significantly higher than that of other comparable structures. The unique flower-like arrangement, sufficient interlayer spacing for Li-ion diffusion, and the increased conductive matrix created using coal-derived graphene enhance the electrode kinetics during electrochemical reactions. Our first-principles calculations revealed that the diffusion barriers are significantly lower in heterostructures compared to that of bare MoS₂. This heterostructure design has significant potential as a new type of anode for Li-ion storage in next-generation batteries.

Ingeniously Designed Yolk-Shell-Structured FeSe2@NDC Nanoboxes as an Excellent Long-Life and High-Rate Anode for Half/Full Na-Ion Batteries

Thanks to their high conductivity and theoretical capacity, transition metal selenides have demanded significant research attention as prospective anodes for sodium-ion batteries. Nevertheless, their practical applications are hindered by finite cycle life and inferior rate performance because of large volume expansion, polyselenide dissolution, and sluggish dynamics. Herein, the nitrogen-doped carbon (NC)-coated FeSe₂ nanoparticles encapsulated in NC nanoboxes (termed FeSe₂@NDC NBs) are fabricated through the facile thermal selenization of polydopamine-wrapped Prussian blue precursors. In this composite, the existing nitrogen-doped dual carbon layer improves the intrinsic conductivity and structural integrity, while the unique porous yolk-shell architecture significantly mitigates the volume swelling during the sodium/desodium process. Moreover, the derived Fe-N-C bonds can effectively capture polyselenide, as well as promote Na⁺ transportation and good reversible conversion reaction. As expected, the FeSe₂@NDC NBs deliver remarkable rate performance (374.9 mA h g^-1 at 10.0 A g^-1) and long-cycling stability (403.3 mA h g^-1 over 2000 loops at 5.0 A g^-1). When further coupled with a self-made Na₃V₂(PO₄)₃@C cathode in sodium-ion full cells, FeSe₂@NDC NBs also exhibit considerably high and stable sodium-storage performance.

Chitosan-Assisted Fabrication of a Network C@V2O5 Cathode for High-Performance Zn-Ion Batteries

Vanadium oxide-based aqueous zinc-ion batteries exhibit promising potential due to their low cost and safety profiles. However, fabricating cathodes with outstanding electrochemical performance for Zn-ion batteries is still a challenge. Herein, network C@V₂O₅ materials were prepared using a mild chitosan-assisted hydrothermal process. Coin-type cells, using network C@V₂O₅ as a cathode, zinc film as an anode, and Zn(CF₃SO₃)₂ as an electrolyte, were also assembled, and the as-synthesized cathode delivered a high specific capacity of 361 mA h g^-1 at 0.5 A g^-1 and excellent cyclic stability. Specifically, after 2000 cycles, the capacity still remained about 71% of the initial value at 0.5 A g^-1. Moreover, ex situ X-ray diffraction (XRD) characterizations confirmed that Zn-ion storage in the cathode was achieved through the reversible intercalation/extraction of Zn²⁺ during the charge/discharge process. Therefore, the network C@V₂O₅ cathode demonstrated potential applications for zinc-ion batteries.

In Situ Formed Weave Cage-Like Nanostructure Wrapped Mesoporous Micron Silicon Anode for Enhanced Stable Lithium-Ion Battery

The low-cost and high-capacity micron silicon is identified as the suitable anode material for high-performance lithium-ion batteries (LIBs). However, the particle fracture and severe capacity fading during electrochemical cycling greatly impede the practical application of LIBs. Herein, we first proposed an in situ reduction and template assembly strategy to attain a weave cage-like carbon nanostructure, composed of short carbon nanotubes and small graphene flakes, as a flexible nanotemplate that closely wrapped micron-sized mesoporous silicon (PSi) to form a robust composite construction. The in situ formed weave cage-like carbon nanostructure can remarkably improve the electrochemical property and structural stability of micron-sized PSi during deep galvanostatic cycling and high electric current density owing to multiple attractive advantages. As a result, the rechargeable LIB applying this anode material exhibits improved initial Coulombic efficiency (ICE), excellent rate performance, and cyclic stability in the existing micron-sized PSi/nanocarbon system. Moreover, this anode reached an approximation of 100% ICE after only three cycles and maintains this level in subsequent cycles. This design of flexible nanotemplated platform wrapped micron-sized PSi anode provides a steerable nanoengineering strategy toward conquering the challenge of long-term reliable LIB application.

Controllable Synthesis of Novel Orderly Layered VMoS2 Anode Materials with Super Electrochemical Performance for Sodium-Ion Batteries

Sodium-ion batteries (SIBs), being an attractive candidate of lithium-ion batteries, have attracted widespread attention as a result of sufficient sodium resource with low price and their comparable suitability in the field of energy storage. However, one of the main challenges for their wide-scale application is to develop suitable anode materials with excellent electrochemical performance. Herein, a novel orderly layered VMoS₂ (OL-VMS) anode material was synthesized through a facile hydrothermal self-assembly approach followed by a heating procedure. As the anode material of the SIBs, the unique structure of OL-VMS not only facilitated the rapid migration of sodium ions between the stacked layers but also provided a stable framework for the volume change in the process of intercalation/deintercalation. In addition, vanadium mediating in the framework caused more defects to produce abundant storage sites for Na⁺. As such, the obtained OL-VMS-based anode exhibited high reversible capacities of 602.9 mAh g^-1 at 0.2 mA g^-1 and 534 mAh g^-1 even after 190-cycle operation at 2 A g^-1. Furthermore, the OL-VMS-based anode delivered an outstanding specific capacity of 626.4 mAh g^-1 after 100-cycle testing at 2 A g^-1 in a voltage range from 0.01 to 3 V. In particular, even in the absence of conductive carbon, it still showed an excellent specific capacity of 260 mAh g^-1 at 1 A g^-1 after 130 cycles in a 0.3-3 V voltage range, which should contribute to the cost reduction and energy density increase.

Low crystalline 1T-MoS2@S-doped carbon hollow spheres as an anode material for Lithium-ion battery

A low crystalline 1T-MoS₂@S-doped carbon (MoS₂@SC) composite was successfully synthesized via a facile hydrothermal process. The composite is comprised by few-layer 1T-MoS₂ nanosheets covered by an amorphous carbon layer with an expanded interlayer d-spacing of 1.01 nm. This structure is conducive to the fast transport of lithium-ions and volume accommodation during the charge-discharge process when the composite is applied as an anode material for LIBs. Additionally, the high conductivity and layered structure of 1T-MoS₂ also facilitate fast of ion/electron transport, contributing to the improvement of the electrochemical properties. Therefore, this material demonstrated a high rate performance and excellent cycling stability, with the capacities of 847 and 622 mA h g^-1 achieved at the current densities of 0.2 A g^-1 and 2 A g^-1, respectively. Even at a larger current density of 2 A g^-1, MoS₂@SC delivered a high reversible capacity of 659 mA h g^-1 with an average capacity loss of 0.006% per cycle after 500 cycles.

Achieving High Pseudocapacitance Anode by An In Situ Nanocrystallization Strategy for Ultrastable Sodium-Ion Batteries

Conversion/alloying type anodes have shown great promise for sodium-ion batteries (SIBs) because of their high theoretical capacity. However, the poor structural stability derived from the large volume expansion and short lifetime impedes their further practical applications. Herein, we report a novel anode with a pomegranate-like nanostructure of SnP₂O₇ particles homogeneously dispersed in the robust N-doped carbon matrix. For the first time, we make use of in situ self-nanocrystallization to generate ultrafine SnP₂O₇ particles with a short pathway of ions and electrons to promote the reaction kinetics. Ex situ transmission electron microscope (TEM) shows that the average particle size of SnP₂O₇ decreases from 66 to 20 nm successfully based on this unique nanoscale-engineering method. Therefore, the nanoparticles together with the N-doped carbon contribute a high pseudocapacitance contribution. Moreover, the N-doped carbon matrix forms strong interaction with the self-nanocrystallization ultrafine SnP₂O₇ particles, leading to a stable nanostructure without any particle aggregation under a long-cycle operation. Benefiting from these synergistic merits, the SnP₂O₇@C anode shows a high specific capacity of 403 mAh g^-1 at 200 mA g^-1 and excellent cycling stability (185 mAh g^-1 after 4000 cycles at 1000 mA g^-1). This work presents a new route for the effective fabrication of advanced conversion/alloying anodes materials for SIBs.

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.

Engineering stable and fast sodium diffusion route by constructing hierarchical MoS2 hollow spheres

Two-dimensional layered transition metal dichalcogenides, such as MoS₂, have been considered to be a promising anode material for sodium storage. However, their performance have been limited by the sluggish sodium diffusion kinetics. In this work, high performance anode material was obtained through constructing hierarchical MoS₂ nanosheets assembled hollow spheres. The used self-templating method show more feasibility than the commonly reported template removal-involved routes. The prepared hollow structure can also provide rapid and stable electron/sodium ion transport without the assistance of conducting substrates, which enables the MoS₂ anodes exhibit a high specific capacity of 527 mAh g^-1 at 0.1 A g^-1. Even at a high current density of 1 A g^-1, capacity of 357 mAh g^-1 can still be obtained after 500 cycles (capacity retention ~94.5%). This work provides a facile way towards high performance MoS₂ anode materials for sodium-ion battery.

Melamine Foam Derived 2H/1T MoS2 as Flexible Interlayer with Efficient Polysulfides Trapping and Fast Li+ Diffusion to Stabilize Li-S Batteries

Lithium-sulfur (Li-S) batteries featuring high-energy densities are identified as a hopeful energy storage system but are strongly impeded by shuttle effect and sluggish redox chemistry of sulfur cathodes. Herein, annealed melamine foam loaded 2H/1T MoS₂ (CF@2H/1T MoS₂) is prepared as a multifunctional interlayer to inhibit the shuttle effect, improve redox kinetics, and reduce the charge-discharge polarization of Li-S batteries. The CF@2H/1T MoS₂ becomes fragmented structures after assembling the cell, which not only benefits to adsorb and catalyze LiPSs but also to significantly buffer the volume expansion due to a large number of gaps between fragmented structures. Meanwhile, the batteries based on CF@2H/1T MoS₂ interlayer delivers high areal capacity of 5.1 mAh cm^-2 under high sulfur mass loading of 7.6 mg cm^-2 at 0.2 C. Importantly, the experiments of in situ Raman spectra demonstrate that the CF@2H/1T MoS₂ can obviously inhibit the shuttle effect by effectively adsorbing and catalyzing LiPSs. This novel design idea and low-cost melamine foam raw material open up a new way for the application of high-energy density Li-S batteries.

Construction of the POMOF@Polypyrrole Composite with Enhanced Ion Diffusion and Capacitive Contribution for High-Performance Lithium-Ion Batteries

Polyoxometalate (POM) as an "electronic sponge" can store a great number of electrons; however, shortcomings of poor conductivity and solubility in electrolytes cause a significant decrease in specific capacity and poor rate capability. To address the aforementioned disadvantages, a dual strategy was proposed, including coating the conductive polypyrrole (PPy) and utilizing nitrogenous ligands (1,10-phenanthroline monohydrate = 1,10-phen) for metal-organic frameworks (MOFs) to fabricate a [Cu(1,10-phen)(H₂O)₂]₂[Mo₆O₂₀]@PPy (Cu-POMOF@PPy) composite, effectively confining the POM in MOFs to avoid dissolution of POM in the electrolyte and improve electrochemical stability. Simultaneously, the PPy shell could improve the conductivity, contribute extra capacity, and alleviate volume variation of Cu-POMOF during cycling. Therefore, the final Cu-POMOF@PPy composite provides an excellent specific capacity of around 769 mA h g^-1 at 0.1 A g^-1 after 160 cycles and good rate performance, associated with great cycling stability (319 mA h g^-1 at 2 A g^-1 after 500 cycles). Moreover, the electrochemical reaction mechanism of Cu-POMOF@PPy was investigated by ex situ XPS measurements, indicating that storage of electrons results from the reduction/oxidation of Mo atoms (Mo⁶⁺ ↔ Mo⁴⁺) and Cu atoms (Cu²⁺ ↔ Cu⁰). As a consequence, this work not only proposes a novel method for preparing POM-based lithium-ion batteries but also expands the variety of anode materials.

Velour Fabric as an Island-Bridge Architectural Design for Stretchable Textile-Based Lithium-ion Battery Electrodes

The advancement of wearable electronics depends on the seamless integration of lightweight and stretchable energy storage devices with textiles. Integrating brittle energy storage materials with soft and stretchable textiles, however, presents a challenging mechanical mismatch. It is critical to protect brittle energy storage materials from strain-induced damage and at the same time preserve the softness and stretchability of the functionalized e-textile. Here, we demonstrate the strategic use of a warp-knitted velour fabric in an "island-bridge" architectural strain-engineering design to prepare stretchable textile-based lithium-ion battery (LIB) electrodes. The velour fabric consists of a warp-knitted framework and a cut pile. We integrate the LIB electrode into this fabric by solution-based metallization to create the warp-knitted framework current collector "bridges" followed by selective deposition of the brittle electroactive material CuS on the cut pile "islands". As the textile electrode is stretched, the warp-knitted framework current collector elongates, while the electroactive cut pile fibers simply ride along at their anchor points on the framework, protecting the brittle CuS coating from strain and subsequent damage. The textile-based stretchable LIB electrode exhibited excellent electrical and electrochemical performance with a current collector sheet resistance of 0.85 ± 0.06 Ω/sq and a specific capacity of 400 mAh/g at 0.5 C for 300 charging-discharging cycles as well as outstanding rate capability. The electrical performance and charge-discharge cycling stability of the electrode persisted even after 1000 repetitive stretching-releasing cycles, demonstrating the protective functionality of the textile-based island-bridge architectural strain-engineering design.

Abnormal Overcharging during Lithium-Ether Co-Intercalation in a Graphite System: Formation of Shuttling Species by the Reduction of the TFSI Anion

Materializing an ultrafast charging system is one of the crucial technologies for next-generation Li-ion batteries (LIBs). Among many studies aimed at achieving fast charging systems, Li-ether solvent cointercalation into the graphite electrodes in LIB has been identified as a novel concept for achieving high power performance because this system does not consist of the sluggish desolvation step and a resistive solid-electrolyte interface (SEI) layer. Interestingly, while studying the Li-ether solvent cointercalation into graphite electrodes, employing lithium bis-trifluoromethane sulfonimide (LiTFSI) as the Li salt, we observed an abnormal overcharging phenomenon. Here, we screened the specific conditions, under which the abnormal overcharging occurred, and revealed that this abnormal overcharging was attributable to the shuttling mechanism. The formation of shuttling species could have been derived by the reduction of TFSI^- anion. With this understanding of the underlying mechanism, we efficiently suppressed the abnormal overcharging by adding LiNO₃ to the electrolyte. The shuttling and resulting overcharging could be prevented by the synergistic contributions of LiNO₃ and S_xO_y, dissolved in the electrolyte, to the formation of a dense solid LiS_xO_y SEI layer on Li-metal. We expect that this work could be a great reference in analyzing many unsolved phenomena in systems utilizing TFSI^-.

High-Performance Porous Silicon/Nanosilver Anodes from Industrial Low-Grade Silicon for Lithium-Ion Batteries

Silicon (Si) has been considered as one of the most promising candidates for the next-generation lithium-ion battery (LIB) anode materials owing to its huge theoretical specific capacity of 4200 mA h g^-1. However, the practical application of Si anodes in commercial LIBs is facing challenges because of the lack of scalable and cost-effective methods to prepare Si-based anode materials with proper microstructure and competitive electrochemical performances. Herein, we report a facile and scalable method to produce multidimensional porous silicon embedded with a nanosilver particle (pSi/Ag) composite from commercially available low-cost metallurgical-grade silicon (MG-Si) powder. The unique hybrid structure contributes to fast electronic transport and relieves volume change of silicon during the charge-discharge process. The pSi/Ag composite exhibits a large initial discharge capacity (3095 mA h g^-1 at a high current of 1 A g^-1), an excellent cycling performance (1930 mA h g^-1 at 1 A g^-1 after 50 cycles), and outstanding rate capacities (up to 1778 mA h g^-1 at a higher current of 2 A g^-1). After the samples are modified by reduced graphene oxide, the capacities of the pSi/Ag@RGO composite electrode can still be maintained over 1000 mA h g^-1 after 200 cycles. This study provides a simple and effective strategy for production of high-performance anode materials.

Polymer-Derived SiOC Integrated with a Graphene Aerogel As a Highly Stable Li-Ion Battery Anode

Amorphous polymer-derived silicon oxycarbide (SiOC) is an attractive candidate for Li-ion battery anodes, as an alternative to graphite, which is limited to a theoretical capacity of 372 mAh/g. However, SiOC tends to exhibit poor transport properties and cycling performance as a result of sparsely distributed carbon clusters and inefficient active sites. To overcome these limitations, we designed and fabricated a layered graphene/SiOC heterostructure by solvent-assisted infiltration of a polymeric precursor into a modified three-dimensional (3D) graphene aerogel skeleton. The use of a high-melting-point solvent facilitated the precursor's freeze drying, which following pyrolysis yielded SiOC as a layer supported on the surface of nitrogen-doped reduced graphene oxide aerogels. The fabrication method employed here modifies the composition and microstructure of the SiOC phase. Among the studied materials, the highest levels of performance were obtained for a sample of moderate SiOC content, in which the graphene network constituted 19.8 wt % of the system. In these materials, a stable reversible charge capacity of 751 mAh/g was achieved at low charge rates. At high charge rates of 1480 mA/g, the capacity retention was ∼95% (352 mAh/g) after 1000 consecutive cycles. At all rates, Coulombic efficiencies >99% were maintained following the first cycle. Performance across all indicators was majorly improved in the graphene aerogel/SiOC nanocomposites, compared with unsupported SiOC. The performance was attributed to mechanisms across multiple length scales. The presence of oxygen-rich SiO_4-xC_x tetrahedral units and a continuous free-carbon network within the SiOC provides sites for reversible lithiation, while high ionic and electronic transport is provided by the layered graphene/SiOC heterostructure.

Boron-Modified Defect-Rich Molybdenum Disulfide Nanosheets: Reducing Nonspecific Adsorption and Promoting a High Capacity for Isolation of Immunoglobulin G

A new type of boric acid derivative-modified molybdenum disulfide nanosheet was prepared by amination and sulfur chemical grafting, where lipoic acid, lysine, and 5-carboxybenzoboroxole were used as reactants. The two-dimensional composite, abbreviated as MoS₂-Lys-CBX, is an ultrathin nanosheet with a minimum unit of single or few layers. Compared with the original molybdenum disulfide, the nonspecific adhesion of interfering proteins on the surface was reduced, and the adsorption capacity of glycoproteins was enhanced, which was 1682.2 mg g^-1 represented by IgG. The adsorbed IgG can be easily eluted with 0.3 wt % CTAB with an elution efficiency of 94.1%. Circular dichroism spectra indicate no obvious conformation change of IgG during the purification process by the MoS₂-Lys-CBX nanosheets. The as-prepared MoS₂-Lys-CBX nanosheets were then employed for the isolation of IgG from human serum sample, obtaining high-purity light and heavy chains of IgG, as demonstrated by SDS-PAGE assays.

Freestanding Na3V2O2(PO4)2F/Graphene Aerogels as High-Performance Cathodes of Sodium-Ion Full Batteries

Although sodium vanadium fluorophosphate, Na₃(VO_1-xPO₄)₂F_1+2x (0 ≤ x ≤ 1), is a highly promising cathode candidate for sodium-ion batteries because of its stable structure and high working voltage, the low charge diffusion dynamics and the inactive materials used in traditional coating electrodes reduce the energy density of a sodium-ion full battery. Hence, Na₃V₂O₂(PO₄)₂F/graphene aerogels (NVPF/GAs) with a three-dimensional continuous porous network are first prepared by coassembly and freeze-drying. The three-dimensional porous network helps to obtain a high NVPF content of 81 wt %, relieve the volume change for improving the cyclability, and enhance the wettability of the electrode with the electrolyte for accelerating the diffusion dynamics of sodium ions and electrons. As a directly used freestanding cathode without the use of any binder/collector, an optimized freestanding NVPF/GA electrode exhibits excellent cycling and rate performances compared to traditional coating electrodes. The average capacities at current densities of 0.2, 0.5, 1.0, 2.0, and 5.0 C are 135.4, 128.0, 125.1, 121.9, and 115.1 mA h g^-1, respectively. Especially, it maintains a capacity retention of 100% after 1000 cycles at an ultrahigh current of 40 C. A sodium-ion full battery with the NVPF/GA cathode and the Sb/graphene/carbon anode attains a of 82.1 mA h g^-1 without an obvious decline after 100 cycles.

Silicon-Doped Argyrodite Solid Electrolyte Li6PS5I with Improved Ionic Conductivity and Interfacial Compatibility for High-Performance All-Solid-State Lithium Batteries

Argyrodite-type sulfide solid electrolytes (SEs) Li₆PS₅X (X = Cl, Br, I) have attracted considerable interest lately by providing a promising lithium-ion transport capability for its application in all-solid-state lithium batteries (ASSLBs). However, other than Li₆PS₅Cl and Li₆PS₅Br, Li₆PS₅I shows poor ionic conductivity of 10^-7 S cm^-1, which is originated from the I^-/S^2- site ordered arrangement in its structure. Herein, we report a silicon-doped solid electrolyte Li_6+xP_1-xSi_xS₅I in this sulfide class, which can remarkably increase the conductivity to 1.1 × 10^-3 S cm^-1 and lower the activation energy to 0.19 eV as a consequence of changing the structural unit in the argyrodite network. The Li_6+xP_1-xSi_xS₅I solid electrolytes are employed in ASSLBs with Li(Ni_0.8Mn_0.1Co_0.1)O₂ (NCM-811) as cathode and Li metal as an anode to evaluate the electrochemical performance. With x = 0.55, the battery displays an initial discharge capacity of 105 mA h g^-1 at a rate of 0.05C and achieves high Coulombic efficiency. Moreover, chemical reactions occurring on the interfaces of the NCM/SE and Li/SE in regard to the degradation of cell performance are also investigated.

Direct Observation of Li Migration into V5S8: Order to Antisite Disorder Intercalation Followed by the Topotactic-Based Conversion Reaction

Two-dimensional transition-metal dichalcogenides hold great potential in rechargeable lithium-ion batteries. Their electrochemical properties are closely related to the structural evolutions during lithium-ion migration. Understanding these migration/reaction mechanisms is important to help improve battery performance. Herein, we report the real-time and atomic-scale observation of phase transitions during the lithiation and delithiation for V₅S₈ via in situ electron diffraction and high-resolution transmission electron microscopy techniques. We find that the phase transformation proceeds via a sequence of order to antisite disorder intercalation and topotactic-based conversion reaction. During the intercalation reaction, the lithium ion destroys the orderings of the interstitial V with the formation of Li/V antisite. Such a reaction is found to be reversible, i.e., the extraction of lithium from Li_xV₅S₈ leads to the recovery of V orderings. The conversion reaction involves heterogeneous nucleation of Li₂S with 3-20 nm nanodomains, which maintain the crystallographic integrity with Li_xV₅S₈. These findings elucidate the complex interactions between the lithium ion and host V₅S₈ during ionic migration in solids, which should be helpful in understanding the relationship between phase transformation kinetics and battery performance.

Interface Engineering of Silicon/Carbon Thin-Film Anodes for High-Rate Lithium-Ion Batteries

Silicon is one of the most promising alternative active materials for next-generation lithium-ion battery (LIB) applications due to its advantage of high specific capacity. However, the enormous volume variations during lithiation/delithiation still remain to be an obstacle to commercialization. In this work, binder-free pure silicon and silicon/carbon (Si/C) multilayer thin-film electrodes, prepared by scalable one-step magnetron sputtering, are systematically investigated by an interlayer strategy. Herein, we present a rationally structural modification by an amorphous carbon film to enhance the electrical conductivity, mechanical integrity, and electrochemical performance of Si film-based LIBs. Therefore, to maintain the consistency of the direct-contact layer with the electrolyte and current collection, symmetrical Si/C/Si and Si/C/Si/C/Si/C/Si electrodes are deliberately designed to study the influence of embedded carbon. An anode with a carbon content of 10.38 wt % yields an initial discharge specific capacity of 1888.74 mAh g^-1 and a capacity retention of 96.82% (1243.56 mAh g^-1) after 150 cycles at a high current density of 4000 mA g^-1. It also shows that the best rate capability remains 96.0% of the initial capacity in the 70th cycle. At last, three mechanisms are proposed for an in-depth understanding of the interface effect. This work offers a new perspective scheme toward Si/C-based LIBs with a capability of high rate and high energy density.

Enhancing the Performance of a Self-Standing Si/PCNF Anode by Optimizing the Porous Structure

Embedding silicon nanoparticles into carbon nanofibers is one of the effective methods to fabricate a self-standing and binder-free Si-based anode material for lithium-ion batteries. However, the sluggish Li-ion transport limits the electrochemical performance in the regular strategies, especially under high rate conditions. Herein, a kind of silicon nanoparticle in porous carbon nanofiber structures (Si/PCNFs) has been fabricated through a facile electrospinning and subsequent thermal treatment. By adjusting the mass ratio to 0.4:1, a Si/PCNF anode material with an effective Li⁺-migration pathway and excellent structural stability can be obtained, resulting in an optimal electrochemical performance. Although increasing the mass ratio of PEG to PAN further can lead to a larger pore size and can be beneficial to Li⁺ migration, thus being profitable for the rate capacity, the structural stability will get worse at the same time as more defects will form and lead to a weaker C-C binding, thus decrease the cycling stability. Remarkably, the rate capacity reaches 1033.4 mA h g^-1 at the current density of 5 A g^-1, and the cycling capacity is 933.2 mA h g^-1 at 0.5 A g^-1 after 200 cycles, maintaining a retention rate of 80.9% with an initial coulombic efficiency of 83.37%.

Design and Preparation of Carbon Nitride-Based Amphiphilic Janus N-Doped Carbon/MoS2 Nanosheets for Interfacial Enzyme Nanoreactor

Janus amphiphilic particles have gained much attention for their important application value in areas as diverse as interfacial modification, sensors, drug delivery, optics, and actuators. In this work, we prepared Janus amphiphilic nanosheets composed of nitrogen-doped stratiform meso-macroporous carbons (NMC) and molybdenum sulfide (MoS₂) for hydrophilic and hydrophobic sides, respectively. The dicyandiamide and glucose were used as precursors for synthesizing two-dimensional nitrogen-doped meso-macroporous carbons, and the molybdate could be anchored by the functional groups on the surface of carbon layers and then transform into uniformly MoS₂ to form the Janus amphiphilic layer by layer NMC/MoS₂ support. Transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are used to demonstrate the successful preparation of Janus materials. As the typical interfacial enzyme, Candida rugosa lipase (CRL) immobilized on the Janus amphiphilic NMC/MoS₂ support brought forth to improvement of its performance because the Janus nanosheets can be easily attached on the oil-aqueous interface for better catalytic activity (interfacial activation of lipases). The obtained immobilized lipase (NMC/MoS₂@CRL) exhibited satisfactory lipase loading (193.1 mg protein per g), specific hydrolytic activity (95.76 U g^-1), thermostability (at 55 °C, 84% of the initial activity remained after 210 min), pH flexibility, and recyclability (60% of the initial activity remained after nine runs). In terms of its application, the esterification rate of using NMC/MoS₂@CRL (75%) is higher than those of NMC@CRL (20%) and MoS₂@CRL (11.8%) in the "oil-water" biphase and CRL as well as NMC/MoS₂@CRL in the one-phase. Comparing with the free CRL, NMC@CRL, and MoS₂@CRL, the Janus amphiphilic NMC/MoS₂ served as a carrier that exhibited more optimal performance and practicability.

Hierarchically Porous MoS2-Carbon Hollow Rhomboids for Superior Performance of the Anode of Sodium-Ion Batteries

It is always challenging to fabricate two-dimensional transition-metal dichalcogenides into multiple hollow micro-/nanostructures with improved properties for various potential applications. Here, hierarchically porous MoS₂-C hollow rhomboids (MCHRs) have been creatively synthesized via a facile self-templated solvothermal approach. It has been clarified that the obtained MCHRs assembled beneath ultrathin γ-MnS and carbon cohybridized MoS₂ nanosheets under the structural direction of the MnMoO₄·0.49H₂O self-template. The prepared MCHR anode of sodium-ion batteries exhibited a reversible capacity of 506 mA h g^-1 at 0.1 A g^-1, ultrahigh rate capabilities up to 10 A g^-1 with 310 mA h g^-1, and exceptional stability over 3000 cycles. This study provides inspiration for the rational design of hierarchically porous hollow nanostructures with specific geometries as an excellent electrode material for outstanding performance energy storage equipment.

Hyperaccumulation Route to Ca-Rich Hard Carbon Materials with Cation Self-Incorporation and Interlayer Spacing Optimization for High-Performance Sodium-Ion Batteries

The hard carbon (HC) has been emerging as one of the most promising anode materials for sodium-ion batteries (SIBs). Incorporation of cations into the HC lattice proved to be effective to regulate their d-interlayer spacing with a modified SIB performance. However, the complexity and high cost of current synthetic processes limited its large-scale application in SIBs. Through the natural hyperaccumulation process, a cost-effective and scale-up-driven procedure to produce Ca-ion self-incorporated HC materials was proposed by applying tamarind fruits as the precursor with the enrichment of Ca ions. In virtue of one-step pyrolysis, the self-incorporated and well-distributed Ca ions in tamarind fruits had successfully served as the buffer layer to expand the d-interlayer spacing of HC materials. Furthermore, the natural porosity hierarchy could be largely preserved by the optimization of calcination temperature. As a result, the Ca-rich HC material had exhibited the optimized cycling performance (326.7 mA h g^-1 at 50 mA g^-1 and capacity retention rate of 89.40% after 250 cycles) with a high initial Coulombic efficiency of 70.39%. This work provided insight into applying the hyperaccumulation effect of biomass precursors to produce doped HC materials with ion self-incorporation and the optimized d-interlayer spacing, navigating its large-scale application for high-performance SIBs.

Two-dimensional metal-organic frameworks and their derivatives for electrochemical energy storage and electrocatalysis

Two-dimensional (2D) metal-organic frameworks (MOFs) and their derivatives with excellent dimension-related properties, e.g. high surface areas, abundantly accessible metal nodes, and tailorable structures, have attracted intensive attention as energy storage materials and electrocatalysts. A major challenge on the road toward the commercialization of 2D MOFs and their derivatives is to achieve the facile and controllable synthesis of 2D MOFs with high quality and at low cost. Significant developments have been made in the synthesis and applications of 2D MOFs and their derivatives in recent years. In this review, we first discuss the state-of-the-art synthetic strategies (including both top-down and bottom-up approaches) for 2D MOFs. Subsequently, we review the most recent application progress of 2D MOFs and their derivatives in the fields of electrochemical energy storage (e.g., batteries and supercapacitors) and electrocatalysis (of classical reactions such as the HER, OER, ORR, and CO2RR). Finally, the challenges and promising strategies for the synthesis and applications of 2D MOFs and their derivatives are addressed for future development.

Copper sulfide nanostructures and their sodium storage properties

Hexagonal CuS nanosheets and microspheres composed of numerous flakes were successfully prepared by sonochemical and solvothermal methods, respectively.

Fabrication of noble metal nanoparticles decorated on one dimensional hierarchical polypyrrole@MoS2 microtubes

Herein, we present a facile strategy to fabricate noble metal (Ag, Au, Pd) decorated on PPy@MoS₂ microtubes. As a proof of application, the ternary PPy@MoS₂@Au hybrids reveal excellent enzyme-like catalytic performance.

Improving the electrochemical performance of a natural molybdenite/N-doped graphene composite anode for lithium-ion batteries via short-time microwave irradiation

In the present work, low-cost natural molybdenite was used to make a MoS₂/N-doped graphene composite through coulombic attraction with the aid of (3-aminopropyl)-triethoxysilane and the electrochemical performance was greatly improved by solvent-free microwave irradiation for tens of seconds. The characterization results indicated that most (3-aminopropyl)-triethoxysilane can decompose and release N atoms to further improve the N-doping degree in NG during the microwave irradiation. In addition, the surface groups of N-doped graphene were removed and the particle size of MoS₂ was greatly decreased after the microwave irradiation. As a result, the composite electrode prepared with microwave irradiation exhibited a better rate performance (1077.3 mA h g⁻¹ at 0.1C and 638 mA h g⁻¹ at 2C) than the sample prepared without microwave irradiation (1013.6 mA h g⁻¹ at 0.1C and 459.1 mA h g⁻¹ at 2C). Therefore, the present results suggest that solvent-free microwave irradiation is an effective way to improve the electrochemical properties of MoS₂/N-doped graphene composite electrodes. This work also demonstrates that natural molybdenite is a promising low-cost anode material for lithium-ion batteries.

In this work, low-cost natural molybdenite was used to make a MoS₂/N-doped graphene composite with the aid of (3-aminopropyl)-triethoxysilane and the electrochemical performance was greatly improved by solvent-free microwave irradiation.

Confinement-Enhanced Rapid Interlayer Diffusion within Graphene-Supported Anisotropic ReSe2 Electrodes

To enhance interlayer lithium diffusion, we engineer electrodes consisting of epitaxially grown ReSe₂ nanosheets by chemical vapor deposition, supported on three-dimensional (3D) graphene foam, taking advantage of its weak van der Waals coupling and anisotropic crystal structure. We further demonstrate its excellent performance as the anode for lithium-ion battery and catalyst for hydrogen evolution reaction (HER). Density functional theory calculation reveals that ReSe₂ exhibits a low energy barrier for lithium (Li) interlayer diffusion because of negligible interlayer coupling and anisotropic structure with low symmetry that creates additional adsorption sites and leads to a reduced diffusion barrier. Benefitting from these properties, the 3D ReSe₂/graphene foam electrode displays excellent cycling and rate performance with 99.6% capacity retention after 350 cycles and a capacity of 327 mA h g^-1 at the current density of 1000 mA g^-1. Additionally, it has exhibited a high activity for HER, in which an exchange current density of 277.8 μA cm^-2 is obtained and only an overpotential of 106 mV is required to achieve a current density of -10 mA cm^-2. Our work provides a fundamental understanding of the interlayer diffusion of Li in transition-metal dichalcogenide (TMD) materials and acts as a new tool for designing a TMD-based catalyst.

Nature-Inspired, Graphene-Wrapped 3D MoS2 Ultrathin Microflower Architecture as a High-Performance Anode Material for Sodium-Ion Batteries

In response to the increasing concern for energy management, molybdenum disulfide (MoS₂) has been extensively researched as an attractive anode material for sodium-ion batteries (SIBs). The proficient cycling durability and good rate performance of SIBs are the two key parameters that determine their potential for practical use. In this study, nature-inspired three-dimensional (3D) MoS₂ ultrathin marigold flower-like microstructures were prepared by a controlled hydrothermal method. These microscale flowers are constructed by arbitrarily arranged but closely interconnected two-dimensional ultrathin MoS₂ nanosheets. The as-prepared MoS₂ microflowers (MFs) have then been chemically wrapped by layered graphene sheets to form the bonded 3D hybrid MoS₂-G networks. TEM, SEM, XRD, XPS, and Raman characterizations were used to study the morphology, crystallization, chemical compositions, and wrapping contact between MoS₂ and graphene. The ultrathin nature of MoS₂ in 3D MFs and graphene wrapping provide strong electrical conductive channels and conductive networks in an electrode. Benefitting from the 2 nm ultrathin crystalline MoS₂ sheets, chemically bonded graphene, defect-induced sodium storage active sites, and 3D interstitial spaces, the prepared electrode exhibited an outstanding specific capacity (606 mA h g^-1 at 200 mA g^-1), remarkable rate performance (345 mA h g^-1 at 1600 mA g^-1), and long cycle life (over 100 cycles with tremendous Coulombic efficiencies beyond 100%). The proposed synthesis strategy and 3D design developed in the present study reveal a unique way to fabricate promising anode materials for SIBs.

In Situ Formation of Co9S8 Nanoclusters in Sulfur-Doped Carbon Foam as a Sustainable and High-Rate Sodium-Ion Anode

Transition-metal sulfides hold great promise as anode materials for sodium-ion batteries due to the high theoretical capacity and excellent redox reversibility based on multielectron conversion reactions. In this work, an elaborate composite, cobalt sulfide nanoclusters embedded in honeycomb-like sulfur-doped carbon foam (Co₉S₈@S-CF), is prepared via a facile sulfur-assisting calcination strategy, which tactfully induces the co-occurrence of in situ pore-forming, sulfidation, sulfur doping, and carbonization. Notably, sulfur-doped carbon foam (S-CF) possesses abundant voids, which are subject to construction of three-dimensional ionic/electronic pathways, leading to high sodium-ion accessibility and ultrafast sodium-ion/electron transportation toward Co₉S₈ nanoclusters. When worked as an anode in sodium-ion batteries, it delivers a remarkable capacity of 373 mA h g^-1 over 1000 cycles at 0.25 C, achieving superior capacity retention of 80%. Furthermore, this anode could achieve unprecedented rate capability with a reversible capacity of 180 mA h g^-1 at 50 C (20 A g^-1), which significantly precedes those reported previously.

Lotus Seedpod-Derived Hard Carbon with Hierarchical Porous Structure as Stable Anode for Sodium-Ion Batteries

Hard carbon material is one of the candidates with great promise as anode-active material for sodium-ion batteries (SIBs). Here, new types of biomass-derived hard carbons were obtained via one-step carbonization of lotus seedpods at 1000-1400 °C, respectively. The control of carbonization temperature proved to be significant in controlling the lattice characterization of lotus seedpod-derived hard carbon. Higher temperature generally promoted the lattice graphitization and thus generated a more narrowed d-interlayer space with limited pore volume. The hard carbon pyrolyzed at 1200 °C achieved an optimized reversible capacity of 328.8 mAh g^-1 and exhibited a remarkable capacity retention of 90% after 200 cycles. In addition, such a biomass-derived hard carbon presented improved cyclic stability and rate performance, revealing capacity of 330.6, 288.9, 216.9, 116.5, and 78.3 mAh g^-1 at 50, 100, 200, 500, and 1000 mA g^-1, respectively. Intrinsically, high pyrolysis temperature (1400 °C) gave rise to more narrowed carbon lattice and reduced pore volume and, thus, failed to accommodate sodium ions either from the intercalation into lattice or the ion adsorption onto the pore surface. Such combined advantages of lotus seedpod-derived hard carbon, including the abundance, sufficiently adequate reversible capacity, and prominent cycling and rate property allowed for its large-scale application as promising anode material for SIBs.