Engineering Hollow Porous Carbon-Sphere-Confined MoS2 with Expanded (002) Planes for Boosting Potassium-Ion Storage

Degradation of molybdenum disulfide through cascade reactions with hydrogen peroxide in aqueous system

Transformation is a crucial process determining the lifespan and risk of MoS2 nanomaterial during usage and after disposal. This study revealed the degradation of MoS2 in the presence of H2O2 using experimental and computational methods. Experimental results showed that MoS2 nanosheets were degraded by 45.1 % after 72-h incubation with H2O2. MoS2 decomposed H2O2 into various reactive oxygen species, among which ·O2- played a dominant role breaking MoS2 into fragments with defects and holes. Mo (IV) in MoS2 catalyzed ·O2- formation through electron transfer towards H2O2. Additionally, electrons generated from cleavage of O-O in H2O2 initiated the O2 reduction to generate ·O2-. The interaction of MoS2 with ·O2- yielded soluble MoO42- and SO42-, and 22.4 % of Mo on residual MoS2 was in the form of Mo (VI) after 72-h incubation. Density function theory calculations elucidated that·O2- is more potent than ·OH in adsorbing on MoS2 ( -2.25 eV vs. -0.14 eV) to initiate reaction. The reaction occurred preferentially from Mo and adjacent S atoms, which transferred 1.07 electrons toward ·O2- to induce O-O cleavage and formation of O-M and O-S bonds. The obtained finding on MoS2 degradation is fundamental for promoting sustainable applications and risk assessment of MoS2-based nanomaterials.

Novel design of nickel cobalt boride nanosheets-decorated molybdenum disulfide hollow spheres as efficient battery-type materials of hybrid supercapacitors

Transition metal borides (TMBs) with high theoretical capacitances and excellent electronic properties have attracted much attention as a promising active material of supercapacitors (SCs). However, TMB nanoparticles are prone to conduct self-aggregation, which significantly deteriorates the electrochemical performance and structural stability. To address the severe self-aggregation in TMBs and improve the active material utilization, it is imperative to provide a conductive substrate that promotes the dispersion of TMB during growths. In this work, sheet-like nickel cobalt boride (NCB) was grown on molybdenum disulfide (MoS2) hollow spheres (H-MoS2) by using simple template growth and chemical reduction methods. The resultant NCB/H-MoS2-50 was observed with uniform NCB nanosheets structure on the surface of the H-MoS2 and stronger MB bonding. After optimizing the loading amount of H-MoS2, the optimal composite (NCB/H-MoS2-50) modified nickel foam (NF) exhibits a superior specific capacity (1302 C/g) than that of the NCB electrode (957 C/g) at 1 A/g. Excellent rate capability of 84.8% (1104 C/g at 40 A/g) is also achieved by the NCB/H-MoS2-50 electrode. The extraordinary electrochemical performance of NCB/H-MoS2-50 is credited to the unique nanosheet-covered hollow spheres structure for facilitating ion diffusion and versatile charge storage mechanisms from the pseudocapacitive behavior of H-MoS2 and the Faradaic redox behavior of NCB. Furthermore, a hybrid SC is assembled with NCB/H-MoS2-50 and activated carbon (AC) electrodes (NCB/H-MoS2-50//AC), which operates in a potential window up to 1.7 V and delivers a high energy density of 76.8 W h kg-1 at a power density of 850 W kg-1. A distinguished cycling stability of 93.2% over 20,000 cycles is also obtained for NCB/H-MoS2-50//AC. These findings disclose the significant potential of NCB/H-MoS2-50 as a highly performed battery-type material of SCs.

Bifunctional electrocatalytic hybrid heterostructures for polysulfide anchoring/conversion for a stable lithium-sulfur battery

In situ phase engineering of transition metal dichalcogenides (TMDs) with controlled sulfur vacancies offers a promising strategy for superior-performance lithium-sulfur (Li-S) batteries. Herein, we demonstrate a bifunctional approach by designing a sulfur host material using 1T-MoS2/MoO3 heterostructures grown directly on carbon nanopot-resembling designer structures (CMS). The metallic phase (1T-MoS2) with MoO3 synergistically contributes to exceptional electronic transport, increased interlayer spacing, and more electrochemically active sites across its basal plane. Carbon nanopot structures and sulfur vacancies within the TMDs act as anchoring sites for lithium polysulfides (LiPSs). Additionally, the specifically phase-engineered 2D heterostructure promotes their efficient conversion into the electrochemically favorable Li2S phase. This dual functionality is expected to significantly improve the rate capability and cycle life stability of Li-S batteries. This translates to a high reversible rate capacity of 1205 mA h g-1 at a current density of 0.2 A g-1. The sulfur-loaded CMS nanostructure shows an excellent cycling life with a decay rate of only 0.078% over 1100 cycles at 1 A g-1, underscoring the effectiveness of the in situ phase engineering approach for creating a stable Li-S battery.

VN Quantum Dots Anchored onto Carbon Nanofibers as a Superior Anode for Sodium Ion Storage

Vanadium-based compounds exhibit a high theoretical capacity to be used as anode materials in sodium-ion batteries, but the volume change in the active ions during the process of release leads to structural instability during the cycle. The structure of carbon nanofibers is stable, while it is difficult to deform. At the same time, the huge specific surface area energy of quantum dot materials can speed up the electrochemical reaction rate. Here, we coupled quantum-grade VN nanodots with carbon nanofibers. The strong coupling of VN quantum dots and carbon nanofibers makes the material have a network structure of interwoven nanofibers. Secondly, the carbon skeleton provides a three-dimensional channel for the rapid migration of sodium ions, and the material has low charge transfer resistance, which promotes the diffusion, intercalation and release of sodium ions, and significantly improves the electrochemical activity of sodium storage. When the material is used as the anode material in sodium ion batteries, the specific capacity is stable at 230.3 mAh g-1 after 500 cycles at 0.5 A g-1, and the specific capacity is still maintained at 154.7 mAh g-1 after 1000 cycles at 2 A g-1.

Yolk-shelled MoS2/C@Void@C@MoS2 nanospheres as a stable and high-rate anode in sodium/potassium ion batteries

We report a yolk-shelled anode material with an MoS2/C core, large inner void and C@MoS2 shell (MoS2/C@Void@C@MoS2). This design could accelerate Na+/K+ reaction kinetics and endure volume changes. Based on the kinetics analysis and calculations based on density functional theory, this structure could effectively enhance the high-rate sodium/potassium storage capability.

Design of heterostructured hydrangea-like FeS2/MoS2 encapsulated in nitrogen-doped carbon as high-performance anode for potassium-ion capacitors

The means of structural hybridization such as heterojunction construction and carbon-coating engineering for facilitating charge transfer and electron transport are considered viable strategies to address the challenges associated with the low rate capability and poor cycling stability of sulfide-based anodes in potassium-ion batteries (PIBs). Motivated by these concepts, we have successfully prepared a hydrangea-like bimetallic sulfide heterostructure encapsulated in nitrogen-doped carbon (FMS@NC) using a simple solvothermal method, followed by poly-dopamine wrapping and a one-step sulfidation/carbonization process. When served as an anode for PIBs, this FMS@NC demonstrates a high specific capacity (585 mAh g-1 at 0.05 A/g) and long cycling stability. Synergetic effects of mitigated volume expansions and enhanced conductivity that are responsbile for such high performance have been verified to originate from the heterostructured sulfides and the N-doped carbon matrix. Meanwhile, comprehensive characterization reveals existence of an intercalation-conversion hybrid K-ion storage mechanism in this material. Impressively, a K-ion capacitor with the FMS@NC anode and a commercial activated carbon cathode exhibits a superior energy density of up to 192 Wh kg-1, a high power density, and outstanding cycling stability. This study provides constructive guidance for designing high-performance and durable potassium-ion storage anodes for next-generation energy storage devices.

MoS2, WS2, and MoWS2 Flakes as Reversible Host Materials for Sodium-Ion and Potassium-Ion Batteries

Transition-metal dichalcogenides (TMDs) and their alloys are vital for the development of sustainable and economical energy storage alternatives due to their large interlayer spacing and hosting ability for alkali-metal ions. Although the Li-ion chemically correlates with the Na-ion and K-ion, research on batteries with TMD anodes for K+ is still in its infancy. This research explores TMDs such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2) and TMD alloys such as molybdenum tungsten disulfide (MoWS2) for both sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs). The cyclic stability test analysis indicates that in the initial cycle, the MoS2 NIB demonstrates exceptional performance, with a peak charge capacity of 1056 mAh g-1, while retaining high Coulombic efficiency. However, the WS2 KIB underperforms, with the least charge capacity of 130 mAh g-1 in the first cycle and exceptionally low retention at a current density of 100 mA g-1. The MoWS2 TMD alloy exhibits a moderate charge capacity and cyclic efficiency for both NIBs and KIBs. This comparison study shows that decreasing sizes of alkali-metal ions and constituent elements in TMDs or TMD alloys leads to decreased resistance and slower degradation processes as indicated by cyclic voltammetry and electrochemical impedance spectroscopy after 10 cycles. Furthermore, the study of probable electrochemical intercalation and removal processes of Na-ions and K-ions demonstrates that large geometrically shaped TMD flakes are more responsive to intercalation for Na-ions than K-ions. These performance comparisons of different TMD materials for NIBs and KIBs may promote the future development of these batteries.

Hollow Nanoreactors for Controlled Photocatalytic Behaviors: Fundamental Theory, Structure-Performance Relationship, and Catalytic Advantages

Hollow nanoreactors (HoNRs) have regarded as an attractive catalytic material for photocatalysis due to their exceptional capabilities in enhancing light harvesting, facilitating charge separation and transfer, and optimizing surface reactions. Developing novel HoNRs offers new options to realize controllable catalytic behavior. However, the catalytic mechanism of photocatalysis occurring in HoNRs has not yet been fully revealed. Against this backdrop, this review elaborates on three aspects: 1) the fundamental theoretical insights of HoNRs-driven photocatalytic kinetics; 2) structure-performance relationship of HoNRs to photocatalysis; 3) catalytic advantages of HoNRs in photocatalytic applications. Specifically, the review focuses on the fundamental theories of HoNRs for photocatalysis and their structural advantages for strengthening light scattering, promoting charge separation and transfer, and facilitating surface reaction kinetics, and the relationship between key structural parameters of HoNRs and their photocatalytic performance is in-depth discussed. Also, future prospects and challenges are proposed. It is anticipated that this review paper will pave the way for forthcoming investigations in the realm of HoNRs for photocatalysis.

Dual carbon engineering enabling 1T/2H MoS2 with ultrastable potassium ion storage performance

Potassium-ion batteries (PIBs) as a promising and low-cost battery technology offer the advantage of utilizing abundant and cost-effective K-salt sources. However, the effective adoption of PIBs necessitates the identification of suitable electrode materials. The 1T phase of MoS2 exhibits enhanced electronic conductivity and greater interlayer spacing compared to the 2H phase, leading to a capable potassium ion storage ability. Herein, we fabricated dual carbon engineered 1T/2H MoS2via a secure and straightforward ammonia-assisted hydrothermal method. The 1T/2H MoS2@rGO@C structure demonstrated an expanded interlayer spacing (9.3 Å). Additionally, the sandwich-like structural design not only enhanced material conductivity but also effectively curbed the agglomeration of nanosheets. Remarkably, 1T/2H MoS2@rGO@C exhibited impressive potassium storage ability, delivering capacities of 351.0 mA h g-1 at 100 mA g-1 and 233.8 mA h g-1 at 1000 mA g-1 following 100 and 1000 cycles, respectively. Moreover, the construction of a K-ion full cell was successfully achieved, utilizing perylene tetracarboxylic dianhydride (PTCDA) as the cathode, and manifesting a capacity of 294.3 mA h g-1 at 100 mA g-1 after 160 cycles. This underscores the substantial potential of employing the 1T/2H MoS2@rGO@C electrode material for PIBs.

Turbostratic Lattice and Electronegativity Modification Jointly Enabled an Ultra-High-Rate and Long-Lived Carbon Anode for Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are considered as a promising technology alternative to lithium-ion batteries due to more abundance of potassium than lithium and a lower redox potential of K/K⁺ than that of Na/Na⁺. The critical limitation in PIBs is the electrode with poor rate capability and cycling stability induced by the sluggish reaction kinetics and large volume change during potassiation and depotassiation. In this work, we report a turbostratic lattice iodine-doped carbon (TLIC) nanosheet as an advanced innovative anode for PIBs displaying fast charge/discharge and electrode stability. The turbostratic lattice caused by doping of large-sized iodine and the unique charge transfer between iodine/carbon atoms creates more active sites and a shorter transport distance for K ions, improves the electrochemical activity, promotes rapid ion diffusion, and enhances pseudocapacitive behavior. The TLIC exhibits a high capacity of 433.5 mAh g^-1 at 50 mA g^-1, an ultrahigh rate capability of 162.1 mAh g^-1 at 20 A g^-1, and an excellent capacity retention of ∼96% (206 mAh g^-1) after 4000 cycles. The combination of turbostratic lattice and pseudocapactive storage is an effective approach to designing carbon electrodes with the transformational performance of high capacity, rate performance, and long lifetime for practical applications of PIBs.

Interlayer-Expanded MoS2 Enabled by Sandwiched Monolayer Carbon for High Performance Potassium Storage

Potassium-ion batteries (PIBs) have aroused a large amount of interest recently due to the plentiful potassium resource, which may show cost benefits over lithium-ion batteries (LIBs). However, the huge volume expansion induced by the intercalation of large-sized potassium ions and the intrinsic sluggish kinetics of the anode hamper the application of PIBs. Herein, by rational design, nano-roses assembled from petals with a MoS2/monolayer carbon (C-MoS2) sandwiched structure were successfully synthesized. The interlayer distance of ultrathin C-MoS2 was expanded from original MoS2 of 6.2 to 9.6 Å due to the formation of the MoS2-carbon inter overlapped superstructure. This unique structure efficiently alleviates the mechanical strain, prevents the aggregation of MoS2, creates more active sites, facilitates electron transport, and enhances the specific capacity and K+ diffusion kinetics. As a result, the prepared C-MoS2-1 anode delivers a high reversible specific capacity (437 mAh g−1 at 0.1 A g−1) and satisfying rate performance (123 mAh g−1 at 6.4 A g−1). Therefore, this work provides new insights into the design of high-performance anode materials of PIBs.

Stabilizing V2O3 in carbon nanofiber flexible films for ultrastable potassium storage

Vanadium oxides, such as V2O3 and VO2, are expected to be potential anode materials for potassium-ion batteries (KIBs) on account of their high theoretical capacity, low price and natural abundance....

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

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

Covalent Pinning of Highly Dispersed Ultrathin Metallic-Phase Molybdenum Disulfide Nanosheets on the Inner Surface of Mesoporous Carbon Spheres for Durable and Rapid Sodium Storage

Two-dimensional (2D) transition-metal dichalcogenide materials show potential for use in alkali metal ion batteries owing to their remarkable physical and chemical properties. Nevertheless, the electrochemical energy storage performance is still impaired by the tendency of aggregation, volume, and morphological change during the conversion reaction and poor intrinsic conductivity. Until now, ultrathin molybdenum disulfide nanosheets with a metallic-phase structure on the inner surface of mesoporous hollow carbon spheres (M-MoS₂@HCS) have rarely been investigated as an anode for sodium-ion batteries. In this work, a novel M-MoS₂@HCS anode was designed and synthesized by employing a template-assisted solvothermal reaction. Structural and chemical analyses indicate that the M-MoS₂ nanosheets with a larger interlayer spacing compared to their semiconductor counterpart grow on the inner surface of HCS via covalent interactions. When used as the anode materials for Na⁺ storage, the M-MoS₂@HCS anode presents durable and rapid sodium storage properties. The developed electrode shows a reversible capacity of 291.2 mAh g^-1 at a high current density of 5 A g^-1. After 100 cycles at 0.1 A g^-1, the reversible capacity is 401.3 mAh g^-1 with a capacity retention rate of 79%. After 2500 cycles at 1.0 A g^-1, the electrode still delivers a reversible capacity of 320.1 mAh g^-1 with a capacity retention rate of 75%. The excellent sodium storage capability of the MoS₂@HCS electrode is explained by the special structural design, which reveals great potential to accelerate the practical applications of transition-metal dichalcogenide electrodes for sodium storage.

An advanced BiPO4/super P anode material for high-performance potassium-ion batteries

Dispersed BiPO₄ nanoparticles loaded on the surface of a super P conducting network (BiPO₄/SP) were fabricated and investigated as a novel anode for PIBs. The BiPO₄/SP electrode demonstrates high rate capability (97.1 mA h g^-1 at 500 mA g^-1) and good long-term cycling performance (116 mA h g^-1 at 200 mA g^-1 over 100 cycles).

Boosting potassium-storage performance via confining highly dispersed molybdenum dioxide nanoparticles within N-doped porous carbon nano-octahedrons

The development of durable and stable metal oxide anodes for potassium ion batteries (PIBs) has been hampered by poor electrochemical performance and ambiguous reaction mechanisms. Herein, we design and fabricate molybdenum dioxide (MoO₂)@N-doped porous carbon (NPC) nano-octahedrons through metal-organic frameworks derived strategy for PIBs with MoO₂ nanoparticles confined within NPC nano-octahedrons. Benefiting from the synergistic effect of nanoparticle level of MoO₂ and N-doped carbon porous nano-octahedrons, the MoO₂@NPC electrode exhibits superior electron/ion transport kinetics, excellent structural integrity, and impressive potassium-ion storage performance with enhanced cyclic stability and high-rate capability. The density functional theory calculations and experiment test proved that MoO₂@NPC has a higher affinity of potassium and higher conductivity than MoO₂ and N-doped carbon electrodes. Kinetics analysis revealed that surface pseudocapacitive contributions are greatly enhanced for MoO₂@NPC nano-octahedrons. In-situ and ex-situ analysis confirmed an intercalation reaction mechanism of MoO₂@NPC for potassium ion storage. Furthermore, the assembled MoO₂@NPC//perylenetetracarboxylic dianhydride (PTCDA) full cell exhibits good cycling stability with 72.6 mAh g^-1 retained at 100 mA g^-1 over 200 cycles. Therefore, this work present here not only evidences an effective and viable structural engineering strategy for enhancing the electrochemical behavior of MoO₂ material in PIBs, but also gives a comprehensive insight of kinetic and mechanism for potassium ion interaction with metal oxide.

A "Biconcave-Alleviated" Strategy to Construct Aspergillus niger-Derived Carbon/MoS2 for Ultrastable Sodium Ion Storage

Two-dimensional layered materials commonly face hindered electron transfer and poor structure stability, thus limiting their application in high-rate and long-term sodium ion batteries. In the current study, we adopt finite element simulation to guide the rational design of nanostructures. By calculating the von Mises stress distribution of a series of carbon materials, we find that the hollow biconcave structure could effectively alleviate the stress concentration resulting from expansion. Accordingly, we propose a biconcave-alleviated strategy based on the Aspergillus niger-derived carbon (ANDC) to construct ANDC/MoS₂ with a hollow biconcave structure. The ANDC/MoS₂ is endowed with an excellent long-term cyclability as an anode of sodium ion batteries, delivering a discharge capacity of 496 mAh g^-1 after 1000 cycles at 1 A g^-1. A capacity retention rate of 94.5% is achieved, an increase of almost seven times compared with the bare MoS₂ nanosheets. Even at a high current density of 5 A g^-1, a reversible discharge capacity around 400 mAh g^-1 is maintained after 300 cycles. ANDC/MoS₂ could also be used for efficient lithium storage. By using in situ TEM, we further reveal that the hollow biconcave structure of ANDC/MoS₂ has enabled stable and fast sodiation/desodiation.

Facile Preparation of MoS2 Nanocomposites for Efficient Potassium-Ion Batteries by Grinding-Promoted Intercalation Exfoliation

Efficient exfoliations of bulk molybdenum disulfide (MoS₂ ) into few-layered nanosheets in pure phase are highly attractive because of the promising applications of the resulted 2D materials in diversified optoelectronic devices. Here, a new exfoliation method is presented to prepare semiconductive 2D hexagonal phase (2H phase) MoS₂ -cellulose nanocrystal (CNC) nanocomposites using grinding-promoted intercalation exfoliation (GPIE). This method with facile grinding of the bulk MoS₂ and CNC powder followed by conventional liquid-phase exfoliation in water can not only efficiently exfoliate 2H-MoS₂ nanosheets, but also produce the 2H-MoS₂ /CNC 2D nanocomposites simultaneously. Interestingly, the intercalated CNC sandwiched in MoS₂ nanosheets increases the interlayer spacing of 2H-MoS₂ , providing perfect conditions to accommodate the large-sized ions. Therefore, these nanocomposites are good anode materials of potassium-ion batteries (KIBs), showing a high reversible capacity of 203 mAh g^-1 at 200 mA g^-1 after 300 cycles, a good reversible capacity of 114 mAh g^-1 at 500 mA g^-1 , and a low decay of 0.02% per cycle over 1500 cycles. With these impressive KIB performances, this efficient GPIE method will open up a new avenue to prepare pure-phase MoS₂ and promising 2D nanocomposites for high-performance device applications.

Nanoscale Ion Regulation in Wood-Based Structures and Their Device Applications

Ion transport and regulation are fundamental processes for various devices and applications related to energy storage and conversion, environmental remediation, sensing, ionotronics, and biotechnology. Wood-based materials, fabricated by top-down or bottom-up approaches, possess a unique hierarchically porous fibrous structure that offers an appealing material platform for multiscale ion regulation. The ion transport behavior in these materials can be regulated through structural and compositional engineering from the macroscale down to the nanoscale, imparting wood-based materials with multiple functions for a range of emerging applications. A fundamental understanding of ion transport behavior in wood-based structures enhances the capability to design high-performance ion-regulating devices and promotes the utilization of sustainable wood materials. Combining this unique ion regulation capability with the renewable and cost-effective raw materials available, wood and its derivatives are the natural choice of materials toward sustainability.

Encapsulating V2O3 Nanoparticles in Hierarchical Porous Carbon Nanosheets via C-O-V Bonds for Fast and Durable Potassium-Ion Storage

Vanadium oxide (V₂O₃) has been considered as a promising anode material for potassium-ion batteries (PIBs), but challenging as well for the low electron/ion conductivity and poor structural stability. To tackle these issues, herein, a novel sheetlike hybrid nanoarchitecture constructed by uniformly encapsulating V₂O₃ nanoparticles in amorphous carbon nanosheets (V₂O₃@C) with the generation of C-O-V bonding is presented. Such a subtle architecture effectively facilitates the infiltration of electrolyte, relieves the mechanical strain, and reduces the potassium-ion diffusion distance during the repetitive charging/discharging processes. The generated C-O-V bonding not only accelerated charge transfer across the carbon-V₂O₃ interface but also strengthened the structural stability. Benefiting from the synergistic effects, the as-prepared V₂O₃@C nanosheets display fast and durable potassium storage behaviors with a reversible capacity of 116.6 mAh g^-1 delivered at 5 A g^-1, and a specific capacity of 147.9 mAh g^-1 retained after 1800 cycles at a high current density of 2 A g^-1. Moreover, the insertion/extraction mechanism of V₂O₃@C nanosheets in potassium-ion storage is systematically demonstrated by electrochemical analysis and ex situ technologies. This study will shed light on the fabricating of other metal oxides anodes for high-performance PIBs and beyond.

MoS2 nanosheets grown on hollow carbon spheres as a strong polysulfide anchor for high performance lithium sulfur batteries

Lithium sulfur batteries are expected to be one of the most promising energy storage systems due to their high energy density, low cost and environmental friendliness. However, the shuttle effect of lithium polysulfides severely hampers their practical application. The design of the sulfur cathode is one of the most important approaches to overcome the problem. In this work, MoS2 nanosheets have been successfully grown on the surface of hollow carbon spheres (HCS) to obtain MoS2@HCS nanocomposites with uniform morphology. The growth behavior of MoS2 nanosheets was also proved by adjusting the pore structure of HCS. With a sulfur loading of 74%, the MoS2@HCS/S cathode exhibits a high initial reversible capacity of 1419 mA h g-1 at a current density of 0.1 C and remains at 1010 mA h g-1 after 100 cycles. Even at 0.5 C, a capacity of 795 mA h g-1 can be retained after 600 cycles, corresponding to a capacity retention rate of 63.1%. By adjusting the concentration of the sulfur source, the relationship between different growth quantities of MoS2 and the cycling performance of the battery was also investigated. The excellent electrochemical performance of the MoS2@HCS/S cathode can be fully attributed to its physical and chemical double adsorption effect on lithium polysulfides, which has been confirmed through the visible adsorption and X-ray Photoelectron Spectroscopy (XPS) experiments. This work provides a simple design concept and method to synthesize a nanocomposite-based sulfur host for high performance lithium sulfur batteries.

Bottom-Up Synthesis of MoS2 /CNTs Hollow Polyhedron with 1T/2H Hybrid Phase for Superior Potassium-Ion Storage

Enslaved to the large-size K-ions, the construction of suitable anode materials with superior and stable potassium-ion storage properties is a major challenge. 1T phase MoS₂ possesses higher conductivity, bigger interlayer distance, and more electrochemically active sites than the 2H phase, which offers intriguing benefits for energy-related applications. In this work, the 1T/2H-phase hybrid MoS₂ nanosheets are successfully anchored in the N-doped carbon nanotube hollow polyhedron (1T/2H-MoS₂ /NCNHP) by a bottom-up solvothermal method. For the synthesized 1T/2H-MoS₂ /NCNHP, the fewer-layer 1T/2H-MoS₂ nanosheets are embedded in an N-doped carbon nanotube hollow polyhedron, with an enlarged interlayer spacing of 0.96 nm. When evaluated as anode material for potassium-ion batteries, the 1T/2H-MoS₂ /NCNHP hybrid presents outstanding potassium storage performance. It delivers a high-specific capacity of 519.2 mAh g^-1 at 50 mA g^-1 and maintains 281.2 mAh g^-1 at 1 A g^-1 over 500 cycles. The good potassium-ion electrochemical performance is attributed to the rational structural design and the synergistic effect of the components. Moreover, the 1T-MoS₂ nanosheet has excellent electrical conductivity and its enlarged interlayer spacing reduces the barrier for the embedding and stripping of K ions. Finally, the practical application of the 1T/2H-MoS₂ /NCNHP electrode material is also evaluated by assembled K-ion full cells.