Two-dimensional nanoarchitectures for lithium storage

Efficient Lithium-Ion Storage by Hierarchical Core-Shell TiO2 Nanowires Decorated with MoO2 Quantum Dots Encapsulated in Carbon Nanosheets

Rational design and surface engineering are the key to synthesizing high-performance electrode materials for electrocatalysis and energy conversion and storage applications. Herein, a novel three-dimensional (3D) nanoarchitecture of TiO₂ nanowires decorated with MoO₂ quantum dots encapsulated in carbon nanosheets was successfully synthesized by a simple polymerization method. Such a hierarchical nanostructure can not only exhibit the synergistic effect of structural stability of a 1D TiO₂ substrate and high capacity of 0D MoO₂ quantum dots but also prevent the aggregation and oxidation of MoO₂. As a result, the novel 0D-1D-2D composite illustrates an initial discharge capacity of 470 mAh g^-1 at a high current density of 500 mA g^-1, especially a capacity retention of about 83% after 450 cycles. The present work highlights the designing strategy of nanoarchitectures containing high capacity materials for enhancing electrochemical performance of Ti-based materials.

Atomic Interface Engineering and Electric-Field Effect in Ultrathin Bi2 MoO6 Nanosheets for Superior Lithium Ion Storage

Ultrathin 2D materials can offer promising opportunities for exploring advanced energy storage systems, with satisfactory electrochemical performance. Engineering atomic interfaces by stacking 2D crystals holds huge potential for tuning material properties at the atomic level, owing to the strong layer-layer interactions, enabling unprecedented physical properties. In this work, atomically thin Bi₂ MoO₆ sheets are acquired that exhibit remarkable high-rate cycling performance in Li-ion batteries, which can be ascribed to the interlayer coupling effect, as well as the 2D configuration and intrinsic structural stability. The unbalanced charge distribution occurs within the crystal and induces built-in electric fields, significantly boosting lithium ion transfer dynamics, while the extra charge transport channels generated on the open surfaces further promote charge transport. The in situ synchrotron X-ray powder diffraction results confirm the material's excellent structural stability. This work provides some insights for designing high-performance electrode materials for energy storage by manipulating the interface interaction and electronic structure.

Two-Dimensional Holey Co3O4 Nanosheets for High-Rate Alkali-Ion Batteries: From Rational Synthesis to in Situ Probing

A general template-directed strategy is developed for the controlled synthesis of two-dimensional (2D) assembly of Co₃O₄ nanoparticles (ACN) with unique holey architecture and tunable hole sizes that enable greatly improved alkali-ion storage properties (demonstrated for both Li and Na ion storage). The as-synthesized holey ACN with 10 nm holes exhibit excellent reversible capacities of 1324 mAh/g at 0.4 A/g and 566 mAh/g at 0.1 A/g for Li and Na ion storage, respectively. The improved alkali-ion storage properties are attributed to the unique interconnected holey framework that enables efficient charge/mass transport as well as accommodates volume expansion. In situ TEM characterization is employed to depict the structural evolution and further understand the structural stability of 2D holey ACN during the sodiation process. The results show that 2D holey ACN maintained the holey morphology at different sodiation stages because Co₃O₄ are converted to extremely small interconnected Co nanoparticles and these Co nanoparticles could be well dispersed in a Na₂O matrix. These extremely small Co nanoparticles are interconnected to provide good electron pathway. In addition, 2D holey Co₃O₄ exhibits small volume expansion (∼6%) compared to the conventional Co₃O₄ particles. The 2D holey nanoarchitecture represents a promising structural platform to address the restacking and accommodate the volume expansion of 2D nanosheets for superior alkali-ion storage.

Holey two-dimensional transition metal oxide nanosheets for efficient energy storage

Transition metal oxide nanomaterials are promising electrodes for alkali-ion batteries owing to their distinct reaction mechanism, abundant active sites and shortened ion diffusion distance. However, detailed conversion reaction processes in terms of the oxidation state evolution and chemical/mechanical stability of the electrodes are still poorly understood. Herein we explore a general synthetic strategy for versatile synthesis of various holey transition metal oxide nanosheets with adjustable hole sizes that enable greatly enhanced alkali-ion storage properties. We employ in-situ transmission electron microscopy and operando X-ray absorption structures to study the mechanical properties, morphology evolution and oxidation state changes during electrochemical processes. We find that these holey oxide nanosheets exhibit strong mechanical stability inherited from graphene oxide, displaying minimal structural changes during lithiation/delithiation processes. These holey oxide nanosheets represent a promising material platform for in-situ probing the electrochemical processes, and could open up opportunities in many energy storage and conversion systems.

As alkali-ion battery anodes, metal oxide nanomaterials suffer from severe structural degradation after charging/discharging cycling. Here the authors develop two-dimensional holey nanosheet anodes which display minimal structural changes during electrochemical operation.

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocatalysis, batteries, supercapacitors, solar cells, photocatalysis, and sensing platforms. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

Large-Area Carbon Nanosheets Doped with Phosphorus: A High-Performance Anode Material for Sodium-Ion Batteries

Large-area phosphorus-doped carbon nanosheets (P-CNSs) are first obtained from carbon dots (CDs) through self-assembly driving from thermal treatment with Na catalysis. This is the first time to realize the conversion from 0D CDs to 2D nanosheets doped with phosphorus. The sodium storage behavior of phosphorus-doped carbon material is also investigated for the first time. As anode material for sodium-ion batteries (SIBs), P-CNSs exhibit superb performances for electrochemical storage of sodium. When cycled at 0.1 A g^-1, the P-CNSs electrode delivers a high reversible capacity of 328 mAh g^-1, even at a high current density of 20 A g^-1, a considerable capacity of 108 mAh g^-1 can still be maintained. Besides, this material also shows excellent cycling stability, at a current density of 5 A g^-1, the reversible capacity can still reach 149 mAh g^-1 after 5000 cycles. This work will provide significant value for the development of both carbon materials and SIBs anode materials.

Chalcogenoether complexes of Nb(v) thio- and seleno-halides as single source precursors for low pressure chemical vapour deposition of NbS2 and NbSe2 thin films

A series of thioether complexes of NbSCl₃ has been prepared and selected examples demonstrated as precursors to 3R-NbS₂ films; deposition of 2H-NbSe₂ from [NbSe₂Cl₃(SeⁿBu₂)] is also reported.

Facile synthesis of nanocrystalline-assembled nest-like NiO hollow microspheres with superior lithium storage performance

Interconnected nest-like NiO hollow microspheres assembled from nanocrystallites are prepared by a facile hydrothermal method followed by annealing at 700 °C in air.

Chemically Integrated Inorganic-Graphene Two-Dimensional Hybrid Materials for Flexible Energy Storage Devices

State-of-the-art energy storage devices are capable of delivering reasonably high energy density (lithium ion batteries) or high power density (supercapacitors). There is an increasing need for these power sources with not only superior electrochemical performance, but also exceptional flexibility. Graphene has come on to the scene and advancements are being made in integration of various electrochemically active compounds onto graphene or its derivatives so as to utilize their flexibility. Many innovative synthesis techniques have led to novel graphene-based hybrid two-dimensional nanostructures. Here, the chemically integrated inorganic-graphene hybrid two-dimensional materials and their applications for energy storage devices are examined. First, the synthesis and characterization of different kinds of inorganic-graphene hybrid nanostructures are summarized, and then the most relevant applications of inorganic-graphene hybrid materials in flexible energy storage devices are reviewed. The general design rules of using graphene-based hybrid 2D materials for energy storage devices and their current limitations and future potential to advance energy storage technologies are also discussed.

Ultrastable nitrogen-doped carbon encapsulating molybdenum phosphide nanoparticles as highly efficient electrocatalyst for hydrogen generation

There is a crucial demand for cost-effective hydrogen evolution reaction (HER) catalysts towards future renewable energy systems, and the development of such catalysts operating under all pH conditions still remains a challenging task. In this work, a one-step facile approach to synthesizing nitrogen-doped carbon encapsulating molybdenum phosphide nanoparticles (MoP NPs@NC) is introduced by using ammonium molybdate, ammonium dihydrogen phosphate and melamine as precursor. Benefitting from structural advantages, including ultrasmall nanoparticles, large exposed surface area and fast charge transfer, MoP NPs@NC exhibits excellent HER catalytic activities with small overpotentials at all pH values (j = 10 mA cm^-2 at η = 115, 136 and 80 mV in 0.5 M H₂SO₄, 1.0 M phosphate buffer solution and 1.0 M KOH, respectively.). Meanwhile, the high catalytic activities of MoP NPs@NC under both neutral and basic conditions have never been achieved before for molybdenum phosphide-based catalysts. Additionally, the encapsulation by N-doped carbon effectively prevents the MoP NPs from corrosion, exhibiting nearly unfading stability after 100 h testing in 0.5 M H₂SO₄. Thus, our work could pave a new avenue for unprecedented design and fabrication of novel low-cost metal phosphide electrocatalysts encapsulated by N-doped carbon.

Ultrathin Zn2(OH)3VO3 Nanosheets: First Synthesis, Excellent Lithium-Storage Properties, and Investigation of Electrochemical Mechanism

Nowadays, exploiting novel electrode materials is widely accepted as a key for meeting the growing demands of high-performance lithium ion batteries. Several transition-metal vanadates, which can in situ form an elastic buffer to adapt the volume expansion during lithium uptake/removal, have recently attracted much attention as anode materials, since they have high capacity and superior cycling stability. Herein, Zn2(OH)3VO3 nanostructures are successfully fabricated for the first time by a facile hydrothermal method and also first studied as lithium ion anode material. The ultrathin Zn2(OH)3VO3 nanosheets deliver a high reversible capacity close to 900 mAh g(-1) at a current density of 1 A g(-1) over 100 cycles. Even at a high current rate of 5 A g(-1), capacity retention as high as 83% (by compared with the second discharge capacity) is still obtained after 500 cycles, showing a high-rate capability. Moreover, we also carefully investigated the lithium-storage mechanism of Zn2(OH)3VO3, and corresponding results reveal that the Zn2(OH)3VO3 nanosheets have in situ transformed into ZnO nanoparticles anchoring on lithiated vanadium oxides matrix. The synergistic effect of zinc and vanadium oxides upon lithium ions intercalation and the stable conductive skeleton of amorphous lithiated vanadium oxides matrix both contribute to the excellent battery performance of Zn2(OH)3VO3 nanosheets. Finally, a full cell composed of lithiated Zn2(OH)3VO3/LiFePO4 with a high energy density of 293 Wh kg(-1) (vs total mass of active materials) at the current density of 100 mA g(-1) was successfully assembled, which could cycle well over 100 cycles with 79% capacity retention and also exhibit good rate stability. Thus, we believe that our research demonstrates a promising anode material for lithium ion batteries.

Recent Progress in Self-Supported Metal Oxide Nanoarray Electrodes for Advanced Lithium-Ion Batteries

The rational design and fabrication of electrode materials with desirable architectures and optimized properties has been demonstrated to be an effective approach towards high-performance lithium-ion batteries (LIBs). Although nanostructured metal oxide electrodes with high specific capacity have been regarded as the most promising alternatives for replacing commercial electrodes in LIBs, their further developments are still faced with several challenges such as poor cycling stability and unsatisfying rate performance. As a new class of binder-free electrodes for LIBs, self-supported metal oxide nanoarray electrodes have many advantageous features in terms of high specific surface area, fast electron transport, improved charge transfer efficiency, and free space for alleviating volume expansion and preventing severe aggregation, holding great potential to solve the mentioned problems. This review highlights the recent progress in the utilization of self-supported metal oxide nanoarrays grown on 2D planar and 3D porous substrates, such as 1D and 2D nanostructure arrays, hierarchical nanostructure arrays, and heterostructured nanoarrays, as anodes and cathodes for advanced LIBs. Furthermore, the potential applications of these binder-free nanoarray electrodes for practical LIBs in full-cell configuration are outlined. Finally, the future prospects of these self-supported nanoarray electrodes are discussed.

Borophene as an extremely high capacity electrode material for Li-ion and Na-ion batteries

"Two-dimensional (2D) materials as electrodes" is believed to be the trend for future Li-ion and Na-ion battery technologies. Here, by using first-principles methods, we predict that the recently reported borophene (2D boron sheets) can serve as an ideal electrode material with high electrochemical performance for both Li-ion and Na-ion batteries. The calculations are performed on two experimentally stable borophene structures, namely β12 and χ3 structures. The optimized Li and Na adsorption sites are identified, and the host materials are found to maintain good electric conductivity before and after adsorption. Besides advantages including small diffusion barriers and low average open-circuit voltages, most remarkably, the storage capacity can be as high as 1984 mA h g(-1) in β12 borophene and 1240 mA h g(-1) in χ3 borophene for both Li and Na, which are several times higher than the commercial graphite electrode and are the highest among all the 2D materials discovered to date. Our results highly support that borophenes can be appealing anode materials for both Li-ion and Na-ion batteries with extremely high power density.

Electrical, Mechanical, and Capacity Percolation Leads to High-Performance MoS2/Nanotube Composite Lithium Ion Battery Electrodes

Advances in lithium ion batteries would facilitate technological developments in areas from electrical vehicles to mobile communications. While two-dimensional systems like MoS2 are promising electrode materials due to their potentially high capacity, their poor rate capability and low cycle stability are severe handicaps. Here, we study the electrical, mechanical, and lithium storage properties of solution-processed MoS2/carbon nanotube anodes. Nanotube addition gives up to 10(10)-fold and 40-fold increases in electrical conductivity and mechanical toughness, respectively. The increased conductivity results in up to a 100× capacity enhancement to ∼1200 mAh/g (∼3000 mAh/cm(3)) at 0.1 A/g, while the improved toughness significantly boosts cycle stability. Composites with 20 wt % nanotubes combine high reversible capacity with excellent cycling stability (e.g., ∼950 mAh/g after 500 cycles at 2 A/g) and high rate capability (∼600 mAh/g at 20 A/g). The conductivity, toughness, and capacity scale with nanotube content according to percolation theory, while the stability increases sharply at the mechanical percolation threshold. We believe that the improvements in conductivity and toughness obtained after addition of nanotubes can be transferred to other electrode materials, such as silicon nanoparticles.

Interface strain in vertically stacked two-dimensional heterostructured carbon-MoS2 nanosheets controls electrochemical reactivity

Two-dimensional (2D) materials offer numerous advantages for electrochemical energy storage and conversion due to fast charge transfer kinetics, highly accessible surface area, and tunable electronic and optical properties. Stacking of 2D materials generates heterogeneous interfaces that can modify native chemical and physical material properties. Here, we demonstrate that local strain at a carbon-MoS₂ interface in a vertically stacked 2D material directs the pathway for chemical storage in MoS₂ on lithium metal insertion. With average measured MoS₂ strain of ∼0.1% due to lattice mismatch between the carbon and MoS₂ layers, lithium insertion is facilitated by an energy-efficient cation-exchange transformation. This is compared with low-voltage lithium intercalation for unstrained MoS₂. This observation implies that mechanical properties of interfaces in heterogeneous 2D materials can be leveraged to direct energetics of chemical processes relevant to a wide range of applications such as electrochemical energy storage and conversion, catalysis and sensing.

Two-dimensional materials are promising for electrochemical energy storage, conversion, catalysis, and sensing. Here the authors leverage strain engineering using a two-dimensional stacked carbon-MoS₂ material to control chemical storage pathways in MoS₂ upon lithium metal insertion.

Oriented-assembly of hollow FePt nanochains with tunable catalytic and magnetic properties

Hollow nanoparticles with large surface areas exhibit a lot of advantages for applications such as catalysis and energy storage. Furthermore, their performance can be manipulated by their deliberate assemblies. Dispersive hollow FePt nanospheres have been assembled into one-dimensional hollow FePt nanochains under the magnetic fields at room temperature. Based on the activation of galvanic replacement at different reaction stages, the size of hollow FePt nanochains can be deliberately manipulated varying from 20 nm to 300 nm, together with the length changing from 200 nm to 10 μm. The competition between movement of paramagnetic Fe(3+) ions and shape recovering due to thermal fluctuations plays a critical effect on the structure of contact area between hollow nanospheres, leading to perforative structures. Compared with commercial Pt/C, well aligned hollow FePt nanochains show greatly enhanced catalytic activities in the methanol oxidation reaction (MOR) due to more favorable mass flow. Magnetic measurements indicate that the magnetic properties including Curie temperature and saturation magnetization can be tuned by the control of the size and shape of hollow nanochains.

Sandwich-like SnS/Polypyrrole Ultrathin Nanosheets as High-Performance Anode Materials for Li-Ion Batteries

Sandwich-like SnS/polypyrrole ultrathin nanosheets were synthesized via a pyrrole reduction and in situ polymerization route, in which room-temperature synthesized ZnSn(OH)6 microcubes were used as the tin source. As anode materials for Li-ion batteries, they exhibit an extremely high reversible capacity (about 1000 mA h g(-1) at 0.1C), outstanding rate capability (with reversible capabilities of 878, 805, 747, 652, and 576 mA h g(-1) at 0.2C, 0.5C, 1C, 2C, and 5C, respectively), stable cycling performance, and high capacity retention (a high capacity of 703 mA h g(-1) at 1C after long 500 cycles).

Three-Dimensional Assembly of Yttrium Oxide Nanosheets into Luminescent Aerogel Monoliths with Outstanding Adsorption Properties

The preparation of macroscopic materials from two-dimensional nanostructures represents a great challenge. Restacking and random aggregation to dense structures during processing prevents the preservation of the two-dimensional morphology of the nanobuilding blocks in the final body. Here we present a facile solution route to ultrathin, crystalline Y2O3 nanosheets, which can be assembled into a 3D network by a simple centrifugation-induced gelation method. The wet gels are converted into aerogel monoliths of macroscopic dimensions via supercritical drying. The as-prepared, fully crystalline Y2O3 aerogels show high surface areas of up to 445 m(2)/g and a very low density of 0.15 g/cm(3), which is only 3% of the bulk density of Y2O3. By doping and co-doping the Y2O3 nanosheets with Eu(3+) and Tb(3+), we successfully fabricated luminescent aerogel monoliths with tunable color emissions from red to green under UV excitation. Moreover, the as-prepared gels and aerogels exhibit excellent adsorption capacities for organic dyes in water without losing their structural integrity. For methyl blue we measured an unmatched adsorption capacity of 8080 mg/g. Finally, the deposition of gold nanoparticles on the nanosheets gave access to Y2O3-Au nanocomposite aerogels, proving that this approach may be used for the synthesis of catalytically active materials. The broad range of properties including low density, high porosity, and large surface area in combination with tunable photoluminescence makes these Y2O3 aerogels a truly multifunctional material with potential applications in optoelectronics, wastewater treatment, and catalysis.

2D transition-metal diselenides: phase segregation, electronic structure, and magnetism

Density-functional theory is used to investigate the phase-segregation behavior of two-dimensional transition-metal dichalcogenides, which are of current interest as beyond-graphene materials for optoelectronic and spintronic applications. Our focus is on the behavior of W1-x V x Se2 monolayers, whose end members are semiconducting WSe2 and ferromagnetic VSe2. The energetics favors phase segregation, but the spinodal decomposition temperature is rather low, about 420 K. The addition of V leads to a transition from a nonmagnetic semiconductor to a metallic ferromagnet, with a ferromagnetic moment of about 1.0 μ B per V atom. The transition is caused by a p-type doping mechanism, which shifts the Fermi level into the valence band. The finite-temperature structure and magnetism of the diselenide systems are discussed in terms of Onsager-type critical fluctuations and Bruggeman effective-medium behavior.

Thickness Dependence and Percolation Scaling of Hydrogen Production Rate in MoS2 Nanosheet and Nanosheet-Carbon Nanotube Composite Catalytic Electrodes

Here we demonstrate that the performance of catalytic electrodes, fabricated from liquid exfoliated MoS2 nanosheets, can be optimized by maximizing the electrode thickness coupled with the addition of carbon nanotubes. We find the current, and so the H2 generation rate, at a given potential to increase linearly with electrode thickness to up ∼5 μm after which saturation occurs. This linear increase is consistent with a simple model which allows a figure of merit to be extracted. The magnitude of this figure of merit implies that approximately two-thirds of the possible catalytically active edge sites in this MoS2 are inactive. We propose the saturation in current to be partly due to limitations associated with transporting charge through the resistive electrode to active sites. We resolve this by fabricating composite electrodes of MoS2 nanosheets mixed with carbon nanotubes. We find both the electrode conductivity and the catalytic current at a given potential to increase with nanotube content as described by percolation theory.

Growth of Lithium Lanthanum Titanate Nanosheets and Their Application in Lithium-Ion Batteries

In this work, lithium-doped lanthanum titanate (LLTO) nanosheets have been prepared by a facile hydrothermal approach. It is found that with the incorporation of lithium ions, the morphology of the product transfers from rectangular nanosheets to irregular nanosheets along with a transition from La2Ti2O7 to Li0.5La0.5TiO3. The as-prepared LLTO nanosheets are used to enhance electrochemical performance of the LiCo1/3Ni1/3Mn1/3O2 (CNM) electrode by forming a higher lithium-ion conductive network. The LiCo1/3Ni1/3Mn1/3O2-Li0.5La0.5TiO3 (CNM-LLTO) electrode shows better a lithium diffusion coefficient of 1.5 × 10(-15) cm(2) s(-1), resulting from higher lithium-ion conductivity of LLTO and shorter lithium diffusion path, compared with the lithium diffusion coefficient of CNM electrode (5.44 × 10(-16) cm(2) s(-1)). Superior reversibility and stability are also found in the CNM-LLTO electrode, which retains a capacity at 198 mAh/g after 100 cycles at a rate of 0.1 C. Therefore, it can be confirmed that the existence of LLTO nanosheets can act as bridges to facilitate the lithium-ion diffusion between the active materials and electrolytes.

One-dimensional metal oxide-carbon hybrid nanostructures for electrochemical energy storage

Numerous metal oxides (MOs) have been considered as promising electrode materials for electrochemical energy storage devices, including lithium-ion batteries (LIBs) and electrochemical capacitors (ECs), because of their outstanding features such as high capacity/capacitance, low cost, as well as environmental friendliness. However, one major challenge for MO-based electrodes is the poor cycling stability derived from the large volume variation and intense mechanic strain, which are inevitably generated during repeated charge/discharge processes. Nanostructure engineering has proven to be one of the most effective strategies to improve the electrochemical performance of MO-based electrode materials. Among various nanostructures, one-dimensional (1D) metal oxide-carbon hybrid nanostructures might offer some solution for the challenging issues involved in bulk MO-based electrode materials for energy storage devices. Herein, we give an overview of the rational design, synthesis strategies and electrochemical properties of such 1D MO-carbon structures and highlight some of the latest advances in this niche area. It starts with a brief introduction to the development of nanostructured MO-based electrodes. We will then focus on the advanced synthesis and improved electrochemical performance of 1D MO-carbon nanostructures with different configurations, including MO-carbon composite nanowires, core-shell nanowires and hierarchical nanostructures. Lastly, we give some perspective on the current challenges and possible future research directions in this area.

Structural Transformation of MXene (V2C, Cr2C, and Ta2C) with O Groups during Lithiation: A First-Principles Investigation

For high capacities and extremely fast charging rates, two-dimensional (2D) crystals exhibit a significant promising application on lithium-ion batteries. With density functional calculations, this paper systematically investigated the Li storage properties of eight 2D M2CO2 (M = V, Cr, Ta, Sc, Ti, Zr, Nb, and Hf), which are the recently synthesized transition-metal carbides (called MXenes) with O groups. According to whether the structural transformation occurs or not during the adsorption of the first Li layer, the adsorption of Li can be grouped into two types: V-type (V2CO2, Cr2CO2, and Ta2CO2) and Sc-type (Sc2CO2, Ti2CO2, Zr2CO2, Nb2CO2, and Hf2CO2). The structural transformation behaviors of V-type are reversible during lithiation/delithiation and are confirmed by ab initio molecular dynamic simulations. Except for Nb-MXene, the V-type prefers the sandwich H2H1T-M2CO2Li4 structure and the Sc-type prefers the TH1H2-M2CO2Li4 structure during the adsorption of the second Li layer. The H2H1T-M2CO2Li4 structure of O layer sandwiched by two Li layers preferred by V-type can prevent forming Li dendrite and therefore stabilize the lithiated system. The tendency of O bonding to Li rather than M in V-type is bigger than that in Sc-type, which causes that the sandwich structure of H2H1T-M2CO2Li4 is more suitable for V-type than Sc-type.

Engineered nanomembranes for smart energy storage devices

This review presents recent progress in engineered tubular and planar nanomembranes for smart energy storage applications, especially related to the investigation of fundamental electrochemical kinetics.

Niobium tetrachloride complexes with thio-, seleno- and telluro-ether coordination – synthesis and structures

Six- and eight-coordinate complexes of NbCl₄ with thio- seleno- and telluro-ethers are described and the structures of representative examples determined.

Solvothermal synthesis and electrochemical properties of S-doped Bi2Se3 hierarchical microstructure assembled by stacked nanosheets

Hierarchical S-doped Bi₂Se₃ microspheres assembled by stacked nanosheets were successfully synthesized as the anode of a lithium ion battery, which shows an initial discharge capacity of 771.3 mA h g⁻¹ with great potential in energy storage.

Ultrafine ferroferric oxide nanoparticles embedded into mesoporous carbon nanotubes for lithium ion batteries

An effective one-pot hydrothermal method for in situ filling of multi-wall carbon nanotubes (CNT, diameter of 20–40 nm, length of 30–100 μm) with ultrafine ferroferric oxide (Fe₃O₄) nanoparticles (8–10 nm) has been demonstrated. The synthesized Fe₃O₄@CNT exhibited a mesoporous texture with a specific surface area of 109.4 m² g⁻¹. The loading of CNT, in terms of the weight ratio of Fe₃O₄ nanoparticles, can reach as high as 66.5 wt%. Compared to the conventional method of using a Al₂O₃ membrane as template to fill CNT with iron oxides nanoparticles, our strategy is facile, effective, low cost and easy to scale up to large scale production (~1.42 g per one-pot). When evaluated for lithium storage at 1.0 C (1 C = 928 mA g⁻¹), the mesoporous Fe₃O₄@CNT can retain at 358.9 mAh g⁻¹ after 60 cycles. Even when cycled at high rate of 20 C, high capacity of 275.2 mAh g⁻¹ could still be achieved. At high rate (10 C) and long life cycling (500 cycles), the cells still exhibit a good capacity of 137.5 mAhg⁻¹.

Two-Dimensional Tin Disulfide Nanosheets for Enhanced Sodium Storage

Sodium-ion batteries (SIBs) are considered as complementary alternatives to lithium-ion batteries for grid energy storage due to the abundance of sodium. However, low capacity, poor rate capability, and cycling stability of existing anodes significantly hinder the practical applications of SIBs. Herein, ultrathin two-dimensional SnS2 nanosheets (3-4 nm in thickness) are synthesized via a facile refluxing process toward enhanced sodium storage. The SnS2 nanosheets exhibit a high apparent diffusion coefficient of Na(+) and fast sodiation/desodiation reaction kinetics. In half-cells, the nanosheets deliver a high reversible capacity of 733 mAh g(-1) at 0.1 A g(-1), which still remains up to 435 mAh g(-1) at 2 A g(-1). The cell has a high capacity retention of 647 mA h g(-1) during the 50th cycle at 0.1 A g(-1), which is by far the best for SnS2, suggesting that nanosheet morphology is beneficial to improve cycling stability in addition to rate capability. The SnS2 nanosheets also show encouraging performance in a full cell with a Na3V2(PO4)3 cathode. In addition, the sodium storage mechanism is investigated by ex situ XRD coupled with high-resolution TEM. The high specific capacity, good rate capability, and cycling durability suggest that SnS2 nanosheets have great potential working as anodes for high-performance SIBs.

Ultrathin Hexagonal 2D Co₂GeO₄ Nanosheets: Excellent Li-Storage Performance and ex Situ Investigation of Electrochemical Mechanism

Two-dimensional (2D) nanostructures are a desirable configuration for lithium ion battery (LIB) electrodes due to their large open surface and short pathway for lithium ions. Therefore, exploring new anode materials with 2D structure could be a promising direction to develop high-performance LIBs. Herein, we synthesized a new type of 2D Ge-based double metal oxides for lithium storage. Ultrathin hexagonal Co2GeO4 nanosheets with nanochannels are prepared by a simple hydrothermal method. When used as LIB anode, the sample delivers excellent cyclability and rate capability. A highly stable capacity of 1026 mAhg(-1) was recorded after 150 cycles. Detailed morphology and phase evolutions were detected by TEM and EELS measurements. It is found that Co2GeO4 decomposed into Ge NPs which are evenly dispersed in amorphous Co/Li2O matrix during the cycling process. Interestingly, the in situ formed Co matrix could serve as a conductive network for electrochemical process of Ge. Moreover, aggregations of Ge NPs could be restricted by the ultrathin configuration and Co/Li2O skeleton, leading to unique structure stability. Hence, the large surface areas, ultrathin thickness, and atomically metal matrix finally bring the superior electrochemical performance.